This is a blog post about an error I found in my /var/log/mail.log file reported by postfix: "SASL authentication failure: cannot connect to saslauthd server: No such file or directory", and the solution I used to resolve it.
First off, this turned out to be a very interesting error! As I explained on the Docunext Wiki Postfix page in the section about using Postfix and Saslauthd on Debian, Postfix processes must run under a chroot.
While the submission service (port 587) in /etc/postfix/master.cf usual runs under a chroot, I had added a new submission directive to relay outgoing messages through dkimproxy:
submission inet n - n - - smtpd -o smtpd_etrn_restrictions=reject -o smtpd_sasl_auth_enable=yes -o content_filter=dksign:[127.0.0.1]:10028 -o receive_override_options=no_address_mappings -o smtpd_recipient_restrictions=permit_mynetworks,permit_sasl_authenticated,reject
For some reason, I had set chroot to "n", and so it was unable to connect to the saslauthd socket!
The resolution for me was to simply change the second "n" to "-", like so:
submission inet n - - - - smtpd