[Dovecot] Why is dovecot involved in my smtp process

[Peter A. Giessel]

> 
> If you are using sendmail as the MTA, Dovecot is not involved for authentication on mail submission.  The maillog line you provided does not contain enough information to tell what triggered the error.

Not totally true. Typical cyrus sasl2 implementation used with sendmail uses an imap server for smtp authentication. I recall having to tweak the sasl2 configuration on my own sendmail server to talk correctly with dovecot. I don't recall the exact tweaks.  I suggest reviewing the sasl2 implementation's documentation (the OP has not to my knowledge stated which sasl implementation he is using). It sounds like an sasl2 problem, not necessarily a dovecot problem.