Guides › Free SMTP Server for Custom Domain Email in 2026

Free SMTP Server for Custom Domain Email in 2026

Updated 2026-10-03 · by Adam Hale

The most generous free SMTP servers for custom domain email in 2026 are Brevo (300 emails a day), Mailjet (6,000 a month, 200 a day), SMTP2GO (1,000 a month), Resend (3,000 a month, 100 a day) and Mailgun (100 a day). Amazon SES no longer has a dedicated free tier for new accounts. All of them need SPF and DKIM records on your domain, and all are built for app and marketing mail rather than personal correspondence. They work for low-volume replies, but read the caveats below.

Free SMTP server for custom domain email in 2026: compared

A personal mailbox typically sends a handful of messages a day, so 100–300 a day is usually plenty. Remember that Bcc-to-self copies count as recipients on services that count each recipient, such as Resend.

Set up SPF, DKIM and DMARC

Each service makes you prove you control the domain. Plan on 15–30 minutes (our estimate) plus DNS propagation.

SPF

SPF is a TXT record on your domain that lists which servers may send for it (RFC 7208).

• Only one SPF record per domain. If you already use a forwarder such as Cloudflare Email Routing, add the sender's include: to the existing record, for example v=spf1 include:_spf.mx.cloudflare.net include:<sender> ~all.
• Keep lookups under 10. Cloudflare's docs note that SPF records are limited to 10 DNS lookups in total.

DKIM

The service gives you one or more CNAME or TXT records holding a public key, and it signs each message with the matching private key (RFC 6376). Because the signature is on your domain, DKIM is usually what makes DMARC pass with these services.

DMARC

DMARC is a TXT record at _dmarc.yourdomain.com that tells receivers what to do when SPF and DKIM don't line up with your From address (RFC 7489). Start with v=DMARC1; p=none; rua=mailto:you@yourdomain.com. Move to quarantine once reports show your mail passing.

Test

Send a message to a Gmail address and open "Show original". SPF, DKIM and DMARC should all show PASS.

Caveats: terms of service and deliverability

• They're built for transactional and marketing mail. Brevo says so plainly, and the others market the same way. (our estimate) None of the terms pages we read bans low-volume personal replies, so they seem to be tolerated. But accounts can be suspended after spam complaints, and support is minimal on free plans.
• Link tracking can rewrite your links. (our estimate) Some services enable click tracking by default, which rewrites links in your messages. Look for tracking settings and turn them off for personal mail. Resend lists open and link tracking among its features; we didn't confirm the defaults.
• Branding footers. (not yet confirmed) Brevo's and Mailjet's pricing pages mention a logo or "Sent with Brevo" footer that paid plans remove. We didn't confirm whether it's added to SMTP mail on free plans, so send yourself a test.
• Shared IP reputation. (our estimate) Free plans send from shared IPs tuned for bulk senders, so inbox placement for one-to-one mail can vary.
• Approval steps. Brevo approves accounts before sending. SMTP2GO limits unverified sender domains to 25 emails an hour, per its support docs.

When a free SMTP relay is the wrong choice

• You want to send as @yahoo.com, @aol.com, @icloud.com or @gmx. Those domains publish strict DMARC policies (p=reject or p=quarantine, checked 2026-10-03). Only the provider's own SMTP server can send as them; see the SMTP app password table.
• You need a real mailbox for your phone or IMAP. Get a cheap host instead: Purelymail ($10/yr), Migadu Micro ($19/yr, 20 outbound a day) or Fastmail ($60/yr).
• It's business-critical mail. Google Workspace Business Starter ($7/user/month on an annual plan) or a paid mailbox gives you support and a reputation you control.
• You'd rather not touch DNS. Workspace or Fastmail will walk you through it with support behind them.

Who holds the key

Google warns that third-party "Send as" tools "often require access to your email credentials" (Gmail Help 17101213). With a free relay, the credential is an SMTP key or SMTP user that only sends mail through that service. It's separate from your account login, and you can revoke it on its own. That's a smaller blast radius than a mailbox password, but still keep it somewhere you control.

How SendAs Relay fits

If you write in Gmail on the web, SendAs Relay can use any of the free senders above for your domain.

• It's a Firefox (140+) and Edge (137+) extension that adds a From picker to Gmail compose. Pick you@yourdomain.com, and the message goes out through Brevo, SMTP2GO, Mailjet, Resend or Mailgun via a stateless relay. Gmail doesn't send it.
• Your SMTP key is stored only in your browser, optionally encrypted with a passphrase.
• The relay is open source (MIT), stores nothing and has logs off. You can deploy it to your own free Cloudflare account.
• Attachments up to about 14 MB in total; a copy can go to Gmail's Sent Mail, or you can Bcc yourself.

It doesn't receive mail, so keep your forwarder, and it doesn't work in the Gmail mobile apps. See how it works and pricing.

Related guides

• Gmail Send mail as removed: what to do
• Custom domain with Gmail without Workspace
• Cloudflare Email Routing: sending from Gmail

Sources

• Brevo pricing, Brevo SMTP relay docs and Brevo SMTP setup help (accessed 2026-10-03)
• Mailjet pricing (accessed 2026-10-03)
• SMTP2GO pricing and SMTP2GO support (accessed 2026-10-03)
• Resend pricing and Resend quotas (accessed 2026-10-03)
• Mailgun pricing (accessed 2026-10-03)
• Amazon SES pricing (accessed 2026-10-03)
• Cloudflare Email Service pricing (updated 2026-06-09) and troubleshooting (accessed 2026-10-03)
• RFC 7208 (SPF), RFC 6376 (DKIM), RFC 7489 (DMARC)
• DMARC records for yahoo.com, aol.com, icloud.com and gmx.net, looked up with dig on 2026-10-03