10 Best Free SMTP Servers for Transactional and Marketing Emails

An SMTP server accepts your outgoing email and relays it to each recipient’s mail server, like a digital post office. An SMTP relay service runs these servers for you: you connect your website or app, and the provider handles delivery, retries, and reporting.

Gmail and other mailbox providers include SMTP for free, but their sending limits are low, so businesses usually need a dedicated service. This guide compares 10 of them by free allowance, rate limits, log retention, and the cost of the first upgrade.

“Free” doesn’t mean the same thing everywhere. Some services give you a permanent free plan, others a trial that ends after a set period, and Amazon SES gives new AWS accounts credits instead. Each offer is labeled below.

Disclosure: UniOne publishes this blog and appears first in this list. UniOne’s offer is a four-month free trial, not a permanent free plan.

Best free SMTP servers at a glance

The table compares what each service gives you for free. It also includes SendGrid and Amazon SES, which now offer a trial and credits rather than permanent free plans.

Service	Best for	Free offer	Free sending allow-ance	Rate limits on the free offer	Logs on the free offer	First paid plan
UniOne	Testing a full feature set at real volume	4-month free trial	6,000 emails/month	No daily or hourly quota listed; SMTP: 5,000/ hour per con-nection	Up to 45 days	$4/ month for 6,000 emails after the trial; next option $6/ month for 10,000
Brevo	Cam-paigns plus transac-tional email	Perma-nent free plan	300 emails/ day	300/day	Un-limited	Starter, $9/ month for 5,000 emails
SMTP2GO	Low-volume transac-tional email	Perma-nent free plan	1,000 emails/month	200/ day; 25/hour until your sender domain is verified	5 days	Starter, $10/ month for 10,000 emails
Mailtrap	Testing emails, then sending them	Perma-nent free plan	4,000 emails/month	150/ day; 150/ hour for new ac-counts	3 days	Basic, $15/ month for 10,000 emails
Mailgun	Deve-lopers who want a mature API	Perma-nent free plan	100 emails /day	100/day	1 day	Basic, $15/ month for 10,000 emails
Mailjet	Building cam-paigns without code	Perma-nent free plan	6,000 emails/month	200/day	Sta-tistics kept 90 days	Starter, $9/ month for 8,000 emails
Mailer-Send	Small apps and proto-types	Perma-nent free plan (app-roval and card required)	500 emails/month	100 API and SMTP re-quests/day	1 day of activity data	Hobby, $7/ month for 5,000 emails
Send-Pulse	Steady, low-rate sending	Perma-nent free SMTP plan	12,000 emails/month	50/hour	1 year of history	Pay as you go, $15 for 10,000 emails
Post-mark	Time-sen-sitive transac-tional email	Perma-nent free Develo-per plan	100 emails/month	No daily cap	Not stated for the free plan	Basic, $15/ month for 10,000 emails
Sender	News-letters plus transac-tional email	Perma-nent free plan	15,000 emails/month, 2,500 sub-scribers	No daily cap	1 day of transac-tional logs	Stan-dard, $9/ month for 500 sub-scribers and 6,000 emails
Send-Grid	Teams ready to pay for scale	60-day free trial	100 emails /day	100/day	3 days	Es-sentials, $19.95/month for 50,000 emails
Amazon SES	Teams already on AWS	Up to $200 in AWS credits, 6-month free plan	Paid from credits	Sand-box: 200 emails per 24 hours, 1 per second	Through event publi-shing	Es-sentials, $0.16 per 1,000 emails

Plan terms checked on vendor websites in October 2026. 

Which free SMTP server fits your use case? 

• WordPress contact forms and password resets: Brevo or SMTP2GO. Both are free mailers in WP Mail SMTP. Brevo allows 300 emails a day, and SMTP2GO queues emails over its daily cap. 

• A SaaS app expecting signup spikes: avoid plans with low hourly caps. UniOne’s trial lists no daily or hourly quota (SMTP allows 5,000 emails per hour per connection), and Mailtrap queues emails over its hourly limit.

• An online store sending receipts and promotions: Sender or Mailjet, which handle campaigns and transactional email in one account. 

• Testing before launch: Mailtrap’s sandbox catches test emails without delivering them. The largest free monthly allowance: Sender, with 15,000 emails a month shared with campaigns. For SMTP sending alone, SendPulse offers 12,000, capped at 50 an hour. 

• Already on AWS: Amazon SES, if you’re comfortable with the sandbox and setup.

How we compared these services

We compared each service on its free allowance, rate limits, what happens at the limit, log retention, and first paid upgrade. Plan terms come from vendor pricing pages and documentation, and ratings from G2, Capterra, and Trustpilot, all checked in October 2026.

We didn’t run our own inbox placement tests. The deliverability percentages in this guide come from EmailToolTester, which ran four rounds of tests with GlockApps, sending to seed addresses at more than 20 mailbox providers. 

EmailToolTester doesn’t say which plans it tested or when each round ran, so the tested plans are unknown. Treat its percentages as service-level results from one test series, not as results for the free plans. UniOne, Mailgun, Sender, and Amazon SES weren’t part of that test.

Free SMTP services reviewed

Each review follows the same format: who the service suits, the free plan’s limits, pros, cons, the first paid upgrade, and what users say.

1. UniOne – best for developers who want a full-featured trial

UniOne is an email delivery service with an SMTP API and a Web API. It suits developers and SaaS teams that want to test every feature at real volume before paying.

Free plan limits

• Offer type: 4-month free trial with 6,000 emails a month and 100 email validations.
• Activation: you activate the trial by adding a credit or debit card in the Billing section.
• Features: everything in the Standard plan, including both APIs, webhooks, templates, and tracking.
• Throughput: the plan lists no daily or hourly quota, but SMTP has a technical limit of 5,000 emails per hour per connection, across up to 10 connections.
• Logs: up to 45 days.

Pros

• Delivery rate: UniOne reports that 99.88% of emails reach their destination. That’s a delivery rate, not an inbox placement figure.
• Scalability: up to 60 million emails per hour through the Web API and 50,000 through SMTP.
• Dedicated IPs: optional, at $40/month plus a $20 setup fee per IP.
• 24/7 support: live chat and email, with an average response time of 5 minutes.

Cons

• Report windows: the Delivery Report covers the last 32 days, and analytics are kept for up to 100 days.
• Templates: some reviewers want more, though UniOne now lists 200+.
• Plain interface: a few reviewers find the design plain.

Pricing

• First paid plan: $4/month for 6,000 emails, which is what the trial plan costs after four months.
• Next tiers: $6/month for 10,000 emails, $11 for 20,000, $25 for 50,000, and $40 for 100,000.
• Extra emails: $0.75 per 1,000 on plans up to 100,000 emails, with lower rates on larger plans.

Source: pricing and plan limits, checked October 2026

User Reviews

UniOne holds 4.7/5 on Capterra from 59 reviews, 4.6/5 on G2 from 25 reviews, and a 4.4 TrustScore on Trustpilot from 12 reviews.

Reviewers praise easy integration, fast delivery, low prices, and responsive support. Criticisms include the plain design and some newsletters landing in spam.

2. Brevo – best for small businesses sending campaigns and transactional email from one account

Brevo is an email marketing and transactional email platform. It was called Sendinblue until May 2023. It suits small businesses that want newsletters and automated emails in one account.

Free plan limits

• Offer type: permanent free plan, no credit card needed, after Brevo approves your account.
• Allowance: 300 emails per day and up to 100,000 contacts, with the API and SMTP relay included.
• Branding: free emails carry the “Sent with Brevo” sticker.
• At the cap: a campaign to more than 300 recipients reaches only 300 that day, and you requeue the rest manually.

Pros

• Long log retention: logs are kept with no time limit by default, even on Free.
• One account for everything: campaigns, automations, and SMTP relay live together.
• WordPress support: Brevo is a free mailer in WP Mail SMTP.

Cons

• Daily cap: 300 emails a day can run out during a signup spike.
• Paid-only features: A/B testing, dedicated IPs, and landing pages aren’t on Free.
• Suspensions: account suspensions are the most frequent complaint on Trustpilot.

Pricing

• First paid plan: Starter, $9/month for 5,000 emails. The Brevo logo stays unless you buy the removal add-on.

Source: pricing and plan limits, checked October 2026

User Reviews

Brevo holds 4.5/5 on G2 from 2,771 reviews, 4.6/5 on Capterra from 3,525 reviews, and 3.8/5 on Trustpilot from 7,248 reviews.

Users like the ease of use and the free tier. Complaints center on suspensions, slow support, and a rigid editor. In EmailToolTester’s tests, Brevo averaged 80%.

3. SMTP2GO – best for low-volume transactional email with strong reporting

SMTP2GO is an outbound-only SMTP relay and email API for small sites and apps that want clear delivery reports.

Free plan limits

• Offer type: permanent free plan, no credit card required.
• Allowance: 1,000 emails per month, capped at 200 per day, and 25 per hour until you verify your sender domain.
• At the caps: emails over the daily cap are queued. Once the monthly allowance is used, new sends are rejected.
• Reporting: 5 days, with chat and phone support for the first 14 days.
• Included on every plan: automatic SPF and DKIM, blacklist monitoring, real-time analytics, and TLS.

Pros

• Visual reports: bounces, unsubscribes, and spam complaints are easy to track.
• Sub-accounts: paid plans support separate limits and settings per sub-account.
• Email testing: the Professional plan previews emails in over 50 email clients.

Cons

• Small allowance: 1,000 emails a month suits low-volume sites only.
• DNS for many domains: users with several sender domains find setup tedious.
• Outbound only: SMTP2GO doesn’t process incoming email.

Pricing

• First paid plan: Starter: $10 per month, or $100 per year, for 10,000 emails per month. Includes 30 days of reporting, chat and phone support, and sub-accounts. Extra emails cost $1 per 1,000.
• Next tier: Professional: $75 per month, or $750 per year, for 100,000 emails per month. Adds a dedicated IP and email testing tools. Extra emails cost $0.85 per 1,000.

Source: pricing and plan limits, checked October 2026

User Reviews

SMTP2GO holds 4.7/5 on G2 from 226 reviews, 4.9/5 on Capterra from 178 reviews, and 4.8/5 on Trustpilot from 1,912 reviews.

Users most often praise easy setup, fast support, and usable reports. Downsides include tedious DNS setup across many domains and occasional throttling delays. In EmailToolTester’s tests, SMTP2GO averaged 96%.

4. Sender – best for small businesses that want newsletters and transactional email on a generous free plan

Sender is an email and SMS marketing platform that also sends transactional email through an API and SMTP. It suits small and growing businesses that want newsletters, automated workflows, and transactional email in one account.

Free plan limits

• Offer type: permanent free plan, no credit card required, with 15,000 emails a month, 2,500 subscribers, and no daily cap.
• Transactional email: included and counted toward the monthly limit, with 1 day of logs. Free emails carry Sender branding.
• Verification: every account goes through a mandatory review that needs company details and a verified domain.
• At the limit: sends stop until the next billing cycle.

Pros

• All in one: transactional email, newsletters, and automation share one platform.
• Ease of use: the drag-and-drop builder suits non-technical users.
• Value: reviewers often call it one of the best-priced options.
• Support: 24/7 live chat and email support on every plan, including the Free plan.

Cons

• Paid-only features: advanced reports and SMS need paid plans.
• Marketing focus: developers wanting a pure SMTP tool may prefer a developer-first service.
• Short logs: one day leaves little time to investigate a failed email.

Pricing

• First paid plan: Standard, $9/month for 500 subscribers and 6,000 emails a month (fewer than Free’s 15,000), billed monthly. It removes Sender branding and adds A/B testing.

Source: pricing and plan limits, checked October 2026

User Reviews

Sender holds 4.7/5 on G2 from 293 reviews, 4.7/5 on Capterra from 212 reviews, and 4.9/5 on Trustpilot from 1,556 reviews.

Users praise its ease of use, support, and free plan. The most common complaint on G2 is limited or dated templates.

5. Mailgun – best for developers who want a mature email API

Mailgun is a developer-focused email API and SMTP relay, now branded Sinch Mailgun. It suits developers who need detailed logs, inbound routing, and API depth more than a large free allowance.

Free plan limits

• Offer type: permanent free plan, 100 emails per day. Foundation and Scale also include one free month.
• Logs: 1 day, with 1 custom sending domain and 2 API keys.
• Credit card: not needed to sign up, but without one you can only send to up to 5 authorized recipients from a sandbox domain.

Pros

• Logs and analytics: reviewers praise them for monitoring performance.
• Documentation: well-structured API docs make implementation easier.
• APIs and webhooks: they support integration and automation of email tasks.

Cons

• Customer support: users report slow, generic responses.
• Cost at volume: pricing gets less economical as volume grows.
• Short logs: free logs expire after a day.

Pricing

• First paid plan: Basic, $15/month for 10,000 emails, with no daily limit.

Source: pricing and plan limits, checked October 2026

User Reviews

Mailgun holds 4.2/5 on G2 from 322 reviews, 4.3/5 on Capterra from 197 reviews, and 4.1/5 on Trustpilot from 1,542 reviews.

When handling transactional emails and email marketing efforts, many value Mailgun’s user-friendliness and dependable delivery. Many users also find its documentation particularly helpful.

However, some users think Mailgun’s customer service could be better. Sinch completed its acquisition of Mailgun’s parent company in December 2021. Since then, some reviewers report a drop in service quality, generic support responses, and slow replies when problems occur. Recent reviews also mention account suspensions and costs that climb with volume.

6. Mailjet – best for marketers who want a simple campaign editor

Mailjet, now Sinch Mailjet, is an email marketing and transactional email service for marketers who want to build campaigns quickly without code.

Free plan limits

• Offer type: permanent free plan, no credit card required, after a 30-day Premium trial.
• Allowance: 6,000 emails per month, capped at 200 per day, with 1,000 contacts.
• At the cap: emails over 200 a day are queued for the next day, but deleted after 3 days.
• Statistics: kept for 90 days. Free emails keep the Mailjet logo.

Pros

• Ease of use: non-technical users can build campaigns quickly.
• Segmentation: you can personalize campaigns by audience segment.
• Integrations: the API connects with multiple CRM systems.

Cons

• Support: customer service is its lowest Capterra sub-rating, at 3.9/5.
• Templates: reviewers find template customization limited.
• Suspensions: some users report accounts suspended without warning.

Pricing

• First paid plan: Starter, $9/month for 8,000 emails and 2,000 contacts, with no daily limit.

Source: pricing and plan limits, checked October 2026

User Reviews

Mailjet holds 3.9/5 on G2 from 175 reviews, 4.2/5 on Capterra from 456 reviews, and 4.0/5 on Trustpilot from 3,994 reviews.

Mailjet’s ease of use lets users with limited technical knowledge create effective email campaigns quickly. Users also appreciate the free plan and the value of paid plans.

Users appreciate the ease of use and the free plan. Complaints include limited templates and slow support. In EmailToolTester’s tests, Mailjet averaged 85%.

7. MailerSend – best for developers who need a small free tier with clean tooling

MailerSend is a transactional email API and SMTP relay from the team behind MailerLite. It suits developers testing a small app who are fine with a low monthly allowance.

Free plan limits

• Offer type: permanent free plan that requires account approval and a credit card, which isn’t charged.
• Allowance: 500 emails per month. The 3,000 figure in older guides belonged to the former free Hobby plan.
• Daily limit: 100 API and SMTP requests per day.
• Limits: 1 verified domain and 1 day of activity data. At the monthly limit, sending pauses until a new period begins.

Pros

• Easy setup: reviewers say the SDKs, SMTP, and API work with little friction.
• Support: users praise quick, human chat support.
• Free trial: you can test the Professional plan for 14 days.

Cons

• Small allowance: 500 emails a month suits testing or very low-volume production projects only.
• Short data window: 1 day of activity data makes debugging hard.
• Card and approval: you need both before sending.

Pricing

First paid plan: Hobby, $7/month for 5,000 emails.

Source: pricing and plan limits, checked October 2026

User Reviews

MailerSend holds 4.1/5 on G2 from 46 reviews, 4.4/5 on Capterra from 62 reviews, and 4.2/5 on Trustpilot from 229 reviews.

Users like the quick setup and support. Complaints focus on suspensions and the pricing change that moved free users to paid plans. In EmailToolTester’s tests, MailerSend averaged 87%.

8. SendPulse – best for steady, low-rate sending at a high monthly volume

SendPulse is a marketing platform with a separate SMTP service for transactional email. It suits senders who need many free emails a month and can spread them evenly through the day.

Free plan limits

• Offer type: permanent free SMTP plan, no credit card required.
• Allowance: 12,000 emails per month, at up to 50 per hour. EmailToolTester also reports a 400-per-day cap, which SendPulse’s own pages don’t state.
• Domains and history: 2 authenticated domains and 1 year of sent-email history.
• Activation: the free plan starts after you authenticate a domain with DKIM and SPF.

Pros

• Large free allowance: the biggest SMTP-only free allowance in this list.
• Long history: a year of logs helps you trace old bounces.
• All-in-one platform: email, SMS, chatbots, and a CRM in one account.

Cons

• Hourly cap: 50 emails an hour can’t absorb sudden bursts of transactional email.
• Limited free support: chat support on Free lasts only 30 days.
• Interface: some reviewers find the UI cluttered.

Pricing

• First paid option: pay as you go, $15 for 10,000 emails, valid for 12 months.

Source: pricing and plan limits, checked October 2026

User Reviews

SendPulse holds 4.6/5 on G2 from 723 reviews, 4.6/5 on Capterra from 773 reviews, and 4.5/5 on Trustpilot from 2,877 reviews.

Users praise the builder, automation, and pricing. Complaints mention slow support and billing issues. In EmailToolTester’s tests, SendPulse averaged 74%.

9. Postmark – best for time-sensitive transactional email at low volume

Postmark is a transactional email service known for fast delivery. It suits apps where password resets and receipts must arrive quickly, if 100 free emails a month is enough to start.

Free plan limits

• Offer type: permanent free Developer plan, no credit card required. It doubles as the trial for paid plans.
• Allowance: 100 emails per month, with no overages and no daily cap.
• Approval: until Postmark approves your account, you can only send to domains you’ve verified.

Pros

• Ease of use: Capterra reviewers rate it 4.9/5.
• Official libraries: Node.js, Python, Ruby, .NET, Java, and PHP.
• Separate streams: transactional and broadcast emails run on separate infrastructure.
• TLS support: Postmark supports TLS to secure connections.

Cons

• Price at low volume: Postmark’s Basic plan costs $15 a month for 10,000 emails, while UniOne charges $6 for the same volume.
• Analytics: reviewers note there’s no link-level click data.
• Small free allowance: 100 emails a month suits testing or very low-volume production projects only.

Pricing

First paid plan: Basic, $15/month for 10,000 emails, with 45-day message retention.

Next tiers: Pro adds inbound processing and retention up to 365 days. Platform removes limits on domains, servers, and users.

Source: pricing and plan limits, checked October 2026

User Reviews

Postmark holds 4.6/5 on G2 from 32 reviews, 4.7/5 on Capterra from 35 reviews, and 2.2/5 on Trustpilot from 45 reviews.

Users say Postmark delivers important emails quickly. Complaints mention higher prices and slow account approvals. In EmailToolTester’s tests, Postmark averaged 94%.

10. Mailtrap – best for teams that test emails before sending them

Mailtrap offers three separate products: Email Sending (API and SMTP), Email Marketing, and an Email Sandbox for testing. It suits development teams that want to test messages safely and then send from the same platform.

Free plan limits

• Offer type: permanent free plans for each product, no credit card required.
• Email Sending: 4,000 emails per month, capped at 150 per day and, for new accounts, 150 per hour.
• At the caps: emails over the hourly limit are queued, while emails over the daily limit are rejected.
• Logs: 3 days, with 1 sending domain.
• Other free plans: Email Marketing allows 500 contacts and 1,500 emails a month, and the Sandbox allows 50 test emails.

Pros

• Strong analytics and debugging: Users praise its deliverability analytics and SMTP error-code debugging.
• User-friendly experience: Ease of use is the top praise theme on G2.
• Responsive customer support: Users consistently highlight the helpfulness of the support team. Capterra reviewers rate customer service 4.9/5.

Cons

• Domain verification speed: One reviewer reported that domain verification took longer than expected.
• Hourly limits for bulk sending: Users report that hourly sending limits slow down peak volumes.
• Short retention on entry plans: Free keeps 3 days of logs, and Basic keeps 5.
• Account reviews: Several Trustpilot reviewers describe accounts blocked during consent checks.

Pricing

• First paid plan: Basic, $15/month for 10,000 emails, with 5 domains and 5-day logs. Sending plans have no contact limits.

Source: pricing and plan limits, checked October 2026

User Reviews

Mailtrap holds 4.8/5 on G2 from 77 reviews, 4.8/5 on Capterra from 36 reviews, and 3.6/5 on Trustpilot from 19 reviews.

Users value the easy setup and friendly interface. Some found the API documentation hard to navigate at first.

Gmail SMTP for personal projects

Gmail’s SMTP server is free with any Google account. It suits personal projects, like a hobby site or a contact form that sends a few messages a day. It’s built for personal mail, though, so treat it separately from the services above. 

• Settings: smtp.gmail.com, port 587 with TLS or port 465 with SSL. Apps sign in with an app password, which requires 2-Step Verification. 
• Personal account limit: sending more than 500 emails in a day, or one email to more than 500 recipients, triggers a block of 1 to 24 hours. The block stops all sending from that account, including your own mail. 
• Google Workspace: 2,000 messages per day per user, at a list price of $7 per user per month for Business Starter. 
• Business use: Google’s Gmail Program Policies ban spam and unsolicited commercial mail, but they don’t explicitly ban business use. Once customers depend on your emails, a dedicated SMTP service gives you higher limits, delivery logs, and your own authenticated domain.

Free trials and paid alternatives

Free offers come in four forms: 

• A permanent free plan with no end date
• A trial for a set period
• credits to spend on usage
• A testing sandbox that catches test emails without delivering them.

SendGrid and Amazon SES used to appear in many free SMTP lists, but both changed their terms in 2025.

SendGrid

Twilio SendGrid is a large email API and SMTP platform. It suits teams that expect to pay and want a mature, scalable service.

Twilio retired SendGrid’s free Email API and Marketing Campaigns plans starting May 27, 2025. New accounts now get a one-time 60-day trial.

Pros

• Dynamic templates: build and personalize templated emails.
• Integrations: official Apollo and third-party HubSpot connectors.
• Security: 2FA, TLS encryption, SOC 2 Type II, and SPF/DKIM authentication.

Cons

• Short activity history: 3 days on Essentials and 7 on Pro, or 30 with a paid add-on.
• Cost at volume: many users find pricing steep for budget-conscious businesses.
• Account freezes: some users report sudden freezes.

Pricing

• Free trial: 100 emails/day for 60 days, no credit card required. Upgrading ends the trial, and it can’t be restarted.
• First paid plan: Essentials, from $19.95/month for 50,000 emails.

Source: pricing and plan limits, checked October 2026

User Reviews

SendGrid holds 4.0/5 on G2 from 369 reviews, 4.2/5 on Capterra from 755 reviews, and 1.1/5 on Trustpilot from 613 reviews.

Users mention scalable infrastructure and easy integration. Criticisms include slow support, costs at volume, and account freezes. In EmailToolTester’s tests, SendGrid averaged 82%.

Amazon SES

Amazon Simple Email Service (SES) is AWS’s pay-as-you-go email service. It suits developers already building on AWS who can handle more setup.

AWS changed its Free Tier on July 15, 2025. New accounts no longer get a monthly SES allowance. They get up to $200 in credits instead.

Pros

• Low cost: à la carte pricing is $0.10 per 1,000 outbound emails.
• AWS integration: connects with Lambda, CloudWatch, and other AWS services.
• IP options: shared, dedicated, and bring-your-own IPs.

Cons

• Setup: it requires a solid understanding of AWS.
• Sandbox: new accounts send only to verified addresses, 200 emails per 24 hours, until AWS grants production access.
• Over the quota: sends that exceed the 24-hour quota are rejected, not queued.
• Marketing features: stored templates through the API, but no A/B testing or visual builder.

Pricing

• Free offer: up to $200 in AWS credits, on a free plan that lasts 6 months or until the credits run out. If you don’t upgrade, the account closes. Accounts created before July 15, 2025 keep the older 3,000 free messages a month for 12 months.
• First paid plan: since July 21, 2026, new accounts start on Essentials at $0.16 per 1,000 emails, with no monthly fee.

Source: pricing and plan limits, checked October 2026

User Reviews

Amazon SES holds 4.3/5 on G2 from 205 reviews, 4.7/5 on Capterra UK from 123 reviews, and 9.2/10 on TrustRadius.

Users appreciate the low cost and reliability, but many find the setup complex and support limited without a paid AWS plan.

How to choose a free SMTP server

Start with your sending pattern, then check the plan terms against it. The questions below cover the limits that trip people up most often.

Free plan, trial, or credits

A permanent free plan suits a side project or a low-volume site that may never pay. A trial suits a business that wants to test a service at real volume before choosing. Credits suit teams that already use the cloud provider.

Read what happens at the end. Mailjet moves trial accounts to its free plan. SendGrid requires an upgrade to keep sending. An AWS free plan account closes if you don’t upgrade.

Monthly allowances vs. daily and hourly limits

A monthly allowance sets how many emails you can send; daily and hourly limits set how fast. Picture a small SaaS app mentioned on a popular forum: 400 people sign up in an hour, and each needs a verification email. On SendPulse’s free plan, you have 12,000 emails a month but only 50 per hour, so the plan can’t send all 400 emails within that hour.

Providers handle overflow differently:

• Queued: SMTP2GO queues emails over its daily cap. Mailjet queues them for the next day but deletes them after 3 days. Mailtrap queues emails over the hourly limit.
• Rejected: Mailtrap rejects emails over its daily limit. Amazon SES rejects sends over the 24-hour quota.
• Paused: MailerSend pauses sending until the next period. Sender stops sends until the next billing cycle.

A rejected email may need your app to retry it.

Log retention

Logs show whether each email was delivered, bounced, or rejected. Say a customer tells you on Monday that a password reset never arrived on Friday. On Mailgun’s free plan, logs last 1 day, so the record is gone. Brevo keeps logs with no time limit by default, and SendPulse keeps a year of SMTP history.

Transactional vs. marketing email

Transactional emails are triggered by one person’s action, like an order confirmation or a password reset. Marketing emails go to a list. An online store needs both as receipts must arrive in seconds, while a promotion can go out over an hour. Sending the two through separate streams keeps complaints about promotions from hurting your receipts. Postmark, for example, runs them on separate infrastructure.

Free plans also count these differently. Sender counts transactional emails toward the same monthly limit as campaigns, while SendPulse and Mailtrap give SMTP and marketing separate free allowances.

Domain authentication and deliverability

Domain authentication proves to mailbox providers that you’re allowed to send from your domain. It uses three DNS records:

• SPF (Sender Policy Framework) lists the servers allowed to send for your domain.
• DKIM (DomainKeys Identified Mail) adds a signature that proves the message wasn’t altered.
• DMARC (Domain-based Message Authentication, Reporting, and Conformance) tells receivers what to do with mail that fails authentication. A message passes DMARC only if SPF or DKIM passes and the passing domain aligns with the domain in the From address.

Gmail’s sender guidelines set two levels. All senders need SPF or DKIM. Bulk senders, meaning those sending close to 5,000 or more messages a day to Gmail accounts, need SPF, DKIM, and DMARC, a From domain aligned with SPF or DKIM, one-click unsubscribe for marketing mail, and a spam rate below 0.3%. Our SPF, DKIM, and DMARC guide walks through the setup.

When you compare deliverability claims, check what’s being measured. A delivery rate counts emails the receiving server accepted. Inbox placement counts emails that reached the inbox instead of the spam folder. 

If you’re already seeing problems, our guide to email deliverability issues covers common fixes.

SMTP or API

Most providers offer HTTP APIs alongside SMTP for more flexibility and speed, but an API means integrating with your code. Basic SMTP, and SMTP with extra features (often called an SMTP API), takes just a few minutes to connect. Use SMTP when your tool already has SMTP settings, like WordPress or a CRM. Use an API when you write the sending code yourself.

Other criteria

• Reliability: check uptime and whether emails go out without delays or failures.
• Scalability: make sure the service can handle spikes of thousands or millions of emails a day.
• Security: look for encrypted SSL/TLS connections and 2FA.
• Ease of use: a clear setup process and an easy-to-navigate dashboard save time.

How to connect and test SMTP

The steps below connect UniOne to a WordPress site using the free WP Mail SMTP plugin, which has over 4 million active installations. The process is similar for the other services in this guide. Only the mailer and SMTP settings in Steps 3 and 4 change.

Step 1: Sign up for UniOne and verify your domain

1. Create a UniOne account. Activate the free trial by adding a credit or debit card in the Billing section.
2. Go to Settings -> Sending domains and click the Add domain button. Enter your sending domain and a tracking subdomain, such as link.yourdomain.com, then click Save.
3. Add the records UniOne shows you at your DNS host: SPF, DKIM, a domain verification TXT record, DMARC, and NS records for the tracking domain.
4. Click the three dots next to your domain and click Verify. Green check marks appear once UniOne finds the records. DNS changes can take from about 30 minutes to several hours.
5. Alternatively, click Get a test domain to receive a free sandbox domain you can use for testing purposes.

UniOne’s DNS setup guide walks through each record.

Step 2: Install the WP Mail SMTP plugin

You can install plugins on a self-hosted WordPress site or on any paid WordPress.com plan.

1. Log in to your WordPress dashboard, go to Plugins, and add a new plugin. Search for “WP Mail SMTP”.
2. Find WP Mail SMTP by WPForms and click Install Now.
3. Click Activate once the installation finishes.

Step 3: Run the Setup Wizard and choose Other SMTP

1. Go to WP Mail SMTP -> Settings and click Launch Setup Wizard. Then click Let’s Get Started.
2. Choose your mailer. The free version of WP Mail SMTP includes mailers for SendLayer, SMTP.com, Gmail / Google Workspace, Brevo, Mailgun, SendGrid, and others. Amazon SES and Microsoft 365 / Outlook.com need the Pro version. For UniOne, select Other SMTP.
3. Click Save and Continue.

Step 4: Enter your UniOne SMTP settings

Fill in the settings screen with these details from UniOne’s SMTP API documentation:

• SMTP Host: smtp.eu1.unione.io if you signed up at eu1.unione.io, or smtp.us1.unione.io if you signed up at us1.unione.io.
• Encryption: TLS (recommended).
• SMTP Port: 587. If your web host blocks port 587, choose SSL with port 465 instead. That connection is still encrypted with TLS from the first byte. UniOne only accepts TLS-encrypted connections.
• Authentication: On.
• SMTP Username: your user_id. You’ll find it in the lower-left corner of the UniOne dashboard.
• SMTP Password: your account API key.
• From Email: an address on the domain you verified in Step 1, such as [email protected].
• From Name: the name recipients see in their inbox, such as your company name or “Support Team”.

If other plugins on your site set their own sender address, turn on Force From Email so every message uses your verified address. To keep your API key out of the WordPress database, you can store it in wp-config.php instead.

Click Save and Continue and finish the remaining screens. The wizard then sends a test email automatically.

Step 5: Send a test email

Email failures are silent. You often learn an email never arrived only when a customer complains. Run a test after setup and whenever you change settings:

1. Go to WP Mail SMTP -> Tools and open the Email Test tab.
2. Enter your email address in the Send To field.
3. Click Send Email and wait a few seconds.
4. Check your inbox and spam folder. If the send fails, the plugin shows an error with details and recommended next steps.

The same page checks your From Email domain’s DNS records. For a closer look at the connection itself, use UniOne’s free SMTP debug tool, which shows the full log of an SMTP session.

Prefer video? This UniOne walkthrough shows how to sign up, verify your domain, and connect the SMTP API to WordPress. For other ways to send from WordPress, including with code, see our guide on how to send emails in WordPress.

Which free SMTP server should you choose?

Start with your sending pattern, which can include how many emails you send, how fast they need to go out, and how long you need logs. The quick picks under the comparison table match common scenarios to services. Then check the first paid upgrade, since growing senders usually outgrow free plans.

The right provider can improve delivery reliability, but sender reputation, domain authentication, and list quality matter just as much.

If you want to test a full feature set at real volume, start a UniOne free trial with 6,000 emails a month for four months.

Frequently Asked Questions

What is the best free SMTP server for a small business?

It depends on how you send. For newsletters plus transactional email, Sender’s free plan includes 15,000 emails a month. For transactional email only, SMTP2GO and Brevo are simple to set up.

Which SMTP services have a permanent free plan?

Brevo, SMTP2GO, Mailtrap, Mailgun, Mailjet, MailerSend, SendPulse, Postmark, and Sender, as of October 2026. UniOne offers a four-month trial, SendGrid a 60-day trial, and Amazon SES AWS credits for new accounts.

Can I use a free SMTP server in production?

Yes, for low volumes, if the limits fit your traffic. Check the hourly and daily caps, what happens to emails over the limit, how long logs last, and whether the plan adds branding or needs account approval.

Is Gmail SMTP free for business use?

Gmail SMTP is free and isn’t banned for business use, but its low sending limits suit personal projects. See Gmail SMTP for personal projects above for the details.

How do I connect a free SMTP server to WordPress?

Install WP Mail SMTP, run its Setup Wizard, choose your provider’s mailer or Other SMTP, and send a test email. The How to connect and test SMTP section has the full steps.

Should I use port 587 or 25 for SMTP connection?

Use port 587 to submit email from your app or website. It’s the standard port for message submission, usually secured with STARTTLS. Port 465 is the alternative for submission over implicit TLS, often called SMTPS. Port 25 is for server-to-server relay, and cloud providers like AWS, Google Cloud, and Azure block or restrict it for outbound traffic. Our guide to SMTP ports covers each one in detail.