Restrict IMAP login, but allow Postfix SASL

[lutz.niederer at gmx.net]

Hi,

we have a very simple user-/passdb (like passwd) to authenticate virtual IMAP users.
We also use this for Postfix authentication.  Nothing special.

But, we need to exclude some of the users from IMAP login.
This means, some users should be allowed to send mail via Postfix (submission) and therefore
authenticate via SASL against dovecot successfully, but they should not be allowed to login
to their IMAP mail box.

How could this be done?

Thanks!
-lutzn