Set up Custom SMTP

Before you start

Use the Custom SMTP option when you want to send through an email server or provider not on Mailrith's prebuilt provider list — for example, a self-hosted mail server, a corporate relay, or a less common ESP that still supports standard SMTP authentication.

Before setting up the connection, gather the following from your SMTP server or provider:

• SMTP hostname: the server address — for example, smtp.example.com.
• Port: common options are 587 (STARTTLS), 465 (TLS/SSL), or 25 (plain, rarely used for modern senders).
• Security mode: whether the server uses STARTTLS, TLS (implicit SSL), or no encryption. This must match what the server actually supports.
• Username and password: the SMTP credentials for the account authorized to send email through this server.

Mailrith fields

When creating a Custom SMTP connection in Mailrith, fill in the following fields:

• SMTP Host: the hostname of your SMTP server, exactly as provided by your server or ESP.
• Port: the SMTP port. Use 587 with STARTTLS or 465 with TLS in most modern configurations.
• Security: choose STARTTLS, TLS, or None to match your server's configuration. STARTTLS is the most common for port 587; TLS is used for port 465.
• Username: the SMTP username — often the full email address of the sending account.
• Password: the SMTP password for authentication.
• From name: the display name in the recipient's inbox.
• From email: the email address in the From field. Must be an address the SMTP server is authorized to send on behalf of.

SMTP server setup

1. In Mailrith, create a new connection and select Custom SMTP.
2. Enter the SMTP host and port exactly as specified by your server or provider.
3. Select the matching security mode. If you are unsure, try STARTTLS with port 587 first — this is the most widely supported combination.
4. Enter the username and password, then fill in the From name and From email.
5. Save the connection and immediately use Send test email to confirm the configuration works.

Testing and troubleshooting

The test email action is especially important for Custom SMTP because there are more configuration variables that can cause failures. Common issues and how to resolve them:

• Connection refused: the host or port is incorrect, or a firewall is blocking outbound connections on that port. Try a different port or confirm network access to the SMTP host.
• Authentication failed: the username or password is wrong. Double-check for copy-paste errors, especially with special characters in passwords.
• TLS handshake error: the selected security mode does not match what the server supports. Switch between STARTTLS and TLS and retry.
• Sender not permitted: the SMTP server is rejecting the From email address. Make sure the address is authorized to send through this server — many servers only allow sending from authenticated account addresses.

Note that Custom SMTP does not support automated bounce and complaint webhook processing. If you use this option, monitor your list hygiene manually or check with your SMTP provider about available notification mechanisms.