Error: Ubuntu/Postfix/Saslauthd - SASL authentication failure: cannot connect to saslauthd server: Permission denied

On a Postfix with SMTP-Auth setup on Ubuntu you see the following error in your mail log:

Apr 26 10:55:19 tcc1 postfix/smtpd[21126]: warning: SASL authentication failure: cannot connect to saslauthd server: Permission denied
Apr 26 10:55:19 tcc1 postfix/smtpd[21126]: warning: SASL authentication failure: Password verification failed
Apr 26 10:55:19 tcc1 postfix/smtpd[21126]: warning: laptop.local[192.168.1.2]: SASL PLAIN authentication failed: generic failure

Solution

Add the postfix user to the sasl group (this makes sure that Postfix has the permission to access saslauthd):

adduser postfix sasl

Then restart Postfix and Saslauthd:

/etc/init.d/postfix restart
/etc/init.d/saslauthd restart