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Enable SMTP

First, enable SMTP for the project you want to use. You can find this setting under your Projects.
Project settings with Enable SMTP option.

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SMTP Configuration

Use these settings to configure your application or email client:
SettingValue
Hostsmtp.lettermint.co
Port587 (see available ports )
AuthenticationPLAIN, LOGIN and CRAM-MD5 are supported
Usernamelettermint
PasswordYour Lettermint API token

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Available ports

Lettermint supports multiple SMTP ports to accommodate different network environments and security requirements:
PortSecurityNotes
25STARTTLS (optional encryption upgrade)Not recommended, blocked by many ISPs and cloud providers
587STARTTLS (encryption upgrade)Recommended for most applications
465Implicit TLS (SMTPS, encrypted from connection start)Good alternative when 587 is blocked
2525STARTTLS (encryption upgrade)Alternative to port 25
2465STARTTLS (encryption upgrade)Alternative to port 465
2587STARTTLS (encryption upgrade)Alternative to port 587

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Understanding TLS Options

  • STARTTLS: Connection starts unencrypted and upgrades to TLS encryption. Used on ports 25, 587, 2525, 2465 and 2587.
  • SMTPS: Connection is encrypted from the start. Used on port 465.
If you’re not sure which port to use, start with port 587. It’s widely accepted and provides good security through STARTTLS.
Port 25 is often blocked by ISPs and cloud providers to prevent spam. We recommend using alternative ports whenever possible.

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Authentication

Authentication is always required when using Lettermint’s SMTP service:
  1. Use your Lettermint API token as both the username and password
  2. Always use TLS encryption (either STARTTLS or Implicit TLS) to protect your credentials
  3. Your API token can be found in your Lettermint dashboard under API settings

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Rate limits

SMTP relay follows the same rate limits as our API:
  • Free tier: 10 emails per day
  • Paid plans: No rate limit

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Testing Your Configuration

Test your SMTP setup with a simple command-line tool: 
# Install swaks (SMTP testing tool)
# On macOS: brew install swaks
# On Ubuntu: apt-get install swaks

swaks --to recipient@example.com \
      --from sender@yourdomain.com \
      --server smtp.lettermint.co:587 \
      --auth LOGIN \
      --auth-user your-api-key \
      --auth-password your-api-key \
      --tls \
      --header "Subject: SMTP Test" \
      --body "This is a test email via SMTP."
For language-specific examples and application configurations, please refer to our dedicated guides in the documentation.