After upgrading a mail server to Debian/Unstable (which will soon be released as Wheezy) I started getting SASL errors.
535 5.7.8 Error: authentication failed: no mechanism available
The SMTP protocol gave the above error for both LOGIN and PLAIN methods.
SASL LOGIN authentication failed: no mechanism available
The postfix/smtpd process logged messages like the above in syslog.
It turned out that the “auxprop_plugin: mysql” line had to be removed and replaced with the following two lines due to a change in the way SQL plugins are managed:
Also the SQL query needed to have “%u” replaced with “%u@%r” because we now have user and realm provided separately.