Last updated: October 2026 | Pricing checked on October 9, 2026 | 10 min read
An SMTP relay service sends email from your website, app or business software through a dedicated, authenticated mail server instead of your own. That matters because emails sent straight from a web server or a shared host often land in spam, or never arrive at all.
We compared eight SMTP relay services on price at 10,000, 50,000 and 100,000 emails a month, free plans and trials, ease of setup and deliverability tools. Prices come from each provider’s pricing page on October 9, 2026.
Our pick for most small businesses and SaaS teams is the Mailercloud Email API. It supports both SMTP relay and a REST API, costs $10/month for 50,000 emails, and comes with a 14-day free trial. Amazon SES is cheaper per email at high volume if you have developers to manage it.
Quick Answer: The Mailercloud Email API is the best SMTP relay service in 2026 for small businesses and SaaS teams: SMTP relay and REST API for $10/month for 50,000 emails (SendGrid Essentials: $19.95), with a 14-day free trial. Amazon SES is cheapest at high volume ($0.10 per 1,000) for developer teams, Postmark is best for fast transactional email, and Mailgun suits teams that need detailed logs.
Table of Contents
What Is an SMTP Relay Service?
SMTP (Simple Mail Transfer Protocol, defined in RFC 5321) is how email moves between servers. An SMTP relay accepts mail from your app or device and delivers it on your behalf, using servers and IP addresses that mailbox providers already trust. Our guide to SMTP explains how the protocol works in more detail.
You use one when you need to send:
- Transactional email: password resets, receipts, order and shipping updates
- App and website notifications: contact form alerts, account messages
- Email from devices and business software: printers, CRMs, help desks, WordPress plugins
Sidenote: An SMTP relay is not the same as an email marketing platform. Relays send the messages your systems generate. For newsletters and campaigns to a list, you need a marketing tool. Some providers, like Mailercloud and Brevo, offer both in one account.
What to Look For
- Price at your volume, including what happens when you go over.
- Authentication support: SPF (RFC 7208), DKIM (RFC 6376) and DMARC (dmarc.org) on your own domain.
- TLS encryption on submission ports 587 or 465 (RFC 8314). See our guide to choosing the right SMTP port.
- Logs and analytics to see what was delivered, bounced or blocked.
- A free plan or trial to test before you commit.
SMTP Relay Services at a Glance
| Service | Best For | Price at 50,000 | Free Option | Standout |
|---|---|---|---|---|
| Mailercloud Email APIOur Pick | SMB & SaaS | $10 (50K) | 14-day trial | SMTP + API |
| Amazon SES | High volume on AWS | $5 (50K) | Pay as you go | $0.10 per 1,000 |
| Postmark | Transactional speed | Scales (from $15/10K) | 100/month | Message streams |
| Mailgun | Logs & inbound | $35 (50K) | 100/day | 30-day logs on Scale |
| SendGrid | Ecosystem | $19.95 (50K) | 60-day trial | SDKs, plugins |
| SMTP2GO | Simple SMTP setup | Scales (from $15) | 1,000/month | Phone support |
| SparkPost | High-volume analytics | $15 (50K) | Test plan | Deep analytics |
| Brevo | Free daily relay | By emails (from $9) | 300/day | Marketing + SMTP |
1. Mailercloud Email API — Best Overall SMTP Relay
The Mailercloud Email API is the best SMTP relay service for small businesses and SaaS teams in 2026. It costs $10/month for 50,000 emails, which is half SendGrid’s Essentials price for the same volume ($19.95). You can send by SMTP relay or REST API, so it works with WordPress plugins, CRMs and custom apps alike.
The same account also gives you Mailercloud’s email marketing platform. That means one vendor and one domain setup for both transactional and marketing email. You also get the email verifier to clean addresses before they bounce, and Inbox Tracker to see where your mail lands.
At 100,000 emails a month you’d move to the $100 plan (500,000 emails), so Mailgun’s Scale plan ($90) is slightly cheaper at exactly that volume. Mailercloud’s integration library is also smaller than SendGrid’s.
Key features
- SMTP relay and REST API
- $10/month for 50,000 emails; $100 for 500,000; $450 for 2.5 million
- 14-day free trial
- SPF, DKIM and DMARC setup for your own domain
- Delivery logs and analytics
- Email marketing, verifier and Inbox Tracker in the same account
✅Mailercloud Email API Pros:
- $10/month for 50,000 emails, half SendGrid Essentials
- SMTP relay and REST API on every plan
- 14-day free trial
- Email marketing, verifier and Inbox Tracker in the same account
- Clear tiers: $100 for 500,000 and $450 for 2.5 million
- SPF, DKIM and DMARC setup for your own domain
❌Mailercloud Email API Cons:
- At exactly 100,000 emails you need the $100 plan (Mailgun Scale is $90)
- Smaller SDK and plugin ecosystem than SendGrid
- No permanent free plan
💰Pricing: $10/month for 50,000 emails; $100 for 500,000; $450 for 2.5M. 14-day free trial.
Pricing: $10/month for 50,000 emails, $100 for 500,000, $450 for 2.5 million; 14-day free trial.
Best for: Small businesses and SaaS teams sending up to 50,000 emails a month.
Try the Mailercloud Email API — SMTP relay and API, $10/month for 50,000 emails, with a 14-day free trial.
2. Amazon SES — Cheapest at High Volume
Amazon Simple Email Service charges $0.10 per 1,000 emails, the lowest per-email price here. That’s $5 for 50,000 emails and $10 for 100,000, plus small charges for attachments and optional extras like dedicated IPs ($24.95/month per IP).
The catch is setup. SES is built for developers. New accounts start in a “sandbox” and must request production access, and logs and analytics need extra AWS services. There’s no support beyond AWS’s paid support plans.
✅Amazon SES Pros:
- Lowest price per email: $0.10 per 1,000
- Scales to very high volume
- Fits naturally if you already use AWS
❌Amazon SES Cons:
- Developer-heavy setup and sandbox approval
- Logs and dashboards need extra AWS services
- No hands-on support without a paid AWS plan
💰Pricing: $0.10 per 1,000 emails; dedicated IPs $24.95/month each.
Best for: Developer teams already on AWS sending at high volume.
3. Postmark — Best for Transactional Speed
Postmark focuses only on transactional email and is known for fast delivery and clear logs. It separates transactional and broadcast mail into different “message streams” to protect deliverability.
The free developer plan covers 100 emails a month. Basic costs $15/month for 10,000 emails, with extra emails at $1.80 per 1,000. Pro and Platform plans ($16.50 and $18 at 10,000) add longer retention and more servers.
✅Postmark Pros:
- Fast, reliable transactional delivery
- Clear, searchable message logs
- Separate streams for transactional and broadcast mail
❌Postmark Cons:
- More expensive per email at higher volume
- Free plan is only 100 emails a month
💰Pricing: Free (100 emails/month); Basic $15/month for 10,000 emails; extra $1.80 per 1,000.
Best for: Apps where password resets and receipts must arrive in seconds.
4. Mailgun — Best for Developers Who Need Logs
Mailgun offers SMTP relay and a powerful API, with flexible inbound routing and email validation. Plans include longer log retention as you move up: 1 day on Basic, 5 days on Foundation and 30 days on Scale.
The free plan allows 100 emails a day. Basic costs $15/month for 10,000 emails, Foundation $35 for 50,000, and Scale $90 for 100,000. Compare it with SendGrid in our SendGrid vs Mailgun comparison.
✅Mailgun Pros:
- Strong API and inbound routing
- 30-day logs on Scale
- Email validation included on higher plans
❌Mailgun Cons:
- Short log retention on Basic (1 day)
- Costs more than Mailercloud at 50,000 emails
💰Pricing: Free (100/day); Basic $15 (10K); Foundation $35 (50K); Scale $90 (100K).
Best for: Developer teams that need detailed logs and inbound email. If Mailgun’s pricing doesn’t fit, see our Mailgun alternatives.
5. SendGrid — Best Ecosystem
Twilio SendGrid has the largest ecosystem of SDKs, plugins and tutorials, and it’s built into many third-party apps. There’s a 60-day free trial (100 emails a day).
Essentials costs $19.95/month for up to 50,000 emails, and Pro $89.95/month for 100,000, which adds a dedicated IP. See our list of SendGrid alternatives if price is a concern.
✅SendGrid Pros:
- Largest ecosystem of SDKs and integrations
- Dedicated IP on Pro
- Marketing Campaigns available in the same account
❌SendGrid Cons:
- No permanent free plan (60-day trial)
- Essentials costs about twice Mailercloud at 50,000 emails
💰Pricing: 60-day trial; Essentials $19.95/month (50K); Pro $89.95/month (100K).
Best for: Teams that need wide SDK and integration support.
6. SMTP2GO — Best for Simple SMTP Setup
SMTP2GO is built around plain SMTP relay, which makes it easy to connect printers, CRMs, WordPress and other business software. It has a free plan for up to 1,000 emails a month, and paid plans start at $15/month. Paid plans include ticket, chat and phone support, and yearly billing gets 2 months free.
✅SMTP2GO Pros:
- Very easy SMTP setup for business software
- Free plan for 1,000 emails a month
- Phone, chat and ticket support on paid plans
❌SMTP2GO Cons:
- Smaller ecosystem than SendGrid or Mailgun
- Reporting is shorter on lower plans (30 days)
💰Pricing: Free (1,000/month); paid from $15/month.
Best for: Small businesses relaying email from everyday software.
7. SparkPost — Best for High-Volume Senders
SparkPost (part of Bird) is built for large senders, with detailed analytics and deliverability insights. The Test plan is free for small volumes. Startup costs from $15/month for 50,000 emails, and Premier from $80/month for 100,000 emails.
✅SparkPost Pros:
- Strong analytics for high-volume senders
- Competitive price at 50,000 emails ($15)
- Free test plan
❌SparkPost Cons:
- Overage per 1,000 emails adds up on small plans
- Interface aimed at technical teams
💰Pricing: Test free; Startup from $15/month (50K); Premier from $80/month (100K).
Best for: High-volume senders who need deep analytics.
8. Brevo — Best Free Daily Allowance
Brevo includes SMTP relay with its email marketing plans. The free plan sends up to 300 emails a day, about 9,000 a month, and paid plans are priced by monthly emails, starting at $9/month for 5,000.
It’s a good fit for small sites that need a free relay for contact forms and order emails, but the daily cap on the free plan can be a problem for bursty traffic.
✅Brevo Pros:
- Free relay for up to 300 emails a day
- Marketing and transactional email in one account
- SMS and WhatsApp available
❌Brevo Cons:
- Daily cap on the free plan
- Paid pricing rises with every email you send
💰Pricing: Free (300/day); Starter from $9/month (5,000 emails).
Best for: Small websites that need a free SMTP relay.
SMTP Relay Pricing at 10,000, 50,000 and 100,000 Emails
Monthly prices from each provider’s pricing page on October 9, 2026.
| Service | 10,000 | 50,000 | 100,000 | Free option |
|---|---|---|---|---|
| Mailercloud Email API | $10 | $10 | $100 (500K plan) | 14-day trial |
| Amazon SES | $1 | $5 | $10 | Pay as you go |
| Postmark | $15 | Scales | Scales | 100/month |
| Mailgun | $15 | $35 | $90 | 100/day |
| SendGrid | $19.95 | $19.95 | $89.95 | 60-day trial |
| SparkPost | — | $15 | $80 | Test plan |
| SMTP2GO | From $15 | Scales | Scales | 1,000/month |
At 50,000 emails a month, only Amazon SES is cheaper than Mailercloud, and SES needs developer time to set up and monitor.
The Mailercloud View: Get the Basics Right Before You Pick a Relay
Most “my emails go to spam” problems aren’t caused by the relay. They come from setup. Before your first send:
- Authenticate your domain. Publish SPF and DKIM records for the relay, then add a DMARC policy. Gmail, Yahoo and Microsoft now require this for bulk senders. See Google’s sender guidelines, Yahoo’s best practices and Microsoft’s requirements.
- Use TLS on port 587 or 465. Avoid port 25, which many hosts block.
- Separate transactional and marketing mail. Use a different subdomain or stream so a marketing complaint spike can’t delay password resets. Our transactional email best practices cover this in more depth.
- Watch bounces. Repeated hard bounces hurt your reputation. Our guide to SMTP 5.7.x bounce codes explains the common errors.
How to Choose
- Up to 50,000 emails a month, want simple pricing: Mailercloud ($10).
- Huge volume, developers on AWS: Amazon SES.
- Transactional speed is critical: Postmark.
- Need logs and inbound routing: Mailgun.
- Need the widest SDK support: SendGrid.
- Relaying from printers, CRMs and plugins: SMTP2GO.
For a broader comparison, see our list of the best transactional email services.
Frequently Asked Questions
What is the best SMTP relay service?
The Mailercloud Email API is the best SMTP relay for most small businesses and SaaS teams in 2026. It costs $10/month for 50,000 emails, supports SMTP and API, and includes a 14-day free trial. Amazon SES is cheapest at very high volume.
Is there a free SMTP relay service?
Yes. Brevo (300 emails a day), SMTP2GO (1,000 a month), Mailgun (100 a day) and Postmark (100 a month) have free plans. Mailercloud and SendGrid offer free trials.
What is the cheapest SMTP relay?
Amazon SES at $0.10 per 1,000 emails. For a managed service with support and a simple dashboard, Mailercloud at $10 for 50,000 emails is one of the cheapest.
What’s the difference between an SMTP relay and an email API?
Both send email through the provider’s servers. SMTP relay works with any software that supports SMTP, with no code. An API gives developers more control and richer responses. Many providers, including Mailercloud, offer both.
Which port should I use for SMTP relay?
Use port 587 with STARTTLS or port 465 with implicit TLS. Port 25 is often blocked by hosting providers and ISPs.
Do I need SPF, DKIM and DMARC for an SMTP relay?
Yes. Without them, Gmail, Yahoo and Microsoft are likely to reject or filter your mail. Every provider here gives you the DNS records to publish.
Final Verdict
The best SMTP relay depends on your volume and your team. Mailercloud gives you SMTP and API sending for $10/month for 50,000 emails, with email marketing in the same account. Amazon SES is cheapest at scale for developer teams, Postmark is best for fast transactional delivery, and Mailgun and SendGrid suit teams that need deep logs or a big ecosystem.
Send 50,000 emails for $10 a month — try the Mailercloud Email API
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Amar CP is the Co-Founder and Sales Director at Mailercloud, where he leads partnerships, alliances, and customer growth. With over a decade of experience in application development, database architecture, and scaling web systems, Amar brings a rare blend of engineering depth and go-to-market expertise to email marketing. He writes about email deliverability, marketing automation, and helping small businesses grow smarter with data-driven campaigns.
