Configuring Postfix to relay through MxGuard

To send your Postfix server's outbound mail through the smarthost using authenticated submission, point its relayhost at MxGuard and give it the generated credentials.

In main.cf:

relayhost = [smtp.mxguard.uk]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = encrypt

The square brackets stop Postfix doing an MX lookup on the smarthost name.

Create /etc/postfix/sasl_passwd:

[smtp.mxguard.uk]:587 your-generated-username:your-generated-password

Then run postmap /etc/postfix/sasl_passwd, secure the files, and reload Postfix.

Finally: add include:_spf.mxguard.uk to your SPF record so the relay's IPs are authorised for your domain. Send a test message and confirm it appears tagged outbound in your dashboard. If you're using IP-allowlist mode instead, drop the SASL lines and connect on port 25 from your registered static IP.