warning: /usr/lib/postfix/smtpd: bad command startup -- throttling

Solution 1:

I think Fedor is right. I have only ever seen that error when Dovecot was configured as the authenticator for Postfix. Make sure dovecot is running and check /var/log/maillog for any issues.

See below for a client server I just fixed that had the exact same errors and messages:

Jul 3 22:12:17mailserver postfix/smtpd[6195]: fatal: no SASL authentication mechanisms Jul 3 22:12:18mailserver postfix/master[4881]: warning: process /usr/libexec/postfix/smtpd pid 6195 exit status 1 Jul 3 22:12:18mailserver postfix/master[4881]: warning: /usr/libexec/postfix/smtpd: bad command startup -- throttling

The fix here was to make sure Dovecot was started, running and configured properly. If you've recently migrated your mail server to a new OS this creates a lot of complications especially with Dovecot sometimes.

Source: http://realtechtalk.com/postfix_errors_fatal_no_SASL_authentication_mechanisms_usrlibexecpostfixsmtpd_bad_command_startup_throttling_solution-2022-articles