[horde] postfix: auth using email-address

[sascha at kredibel.de]

We are using IMP in a shared vhost environment.

I would like to let the customers log-in using their email-addresses  
(or aliases) instead of their IMAP username.

So far I just found solutions using LDAP or mySQL and I was wondering  
if this isn't too complicated.

All postfix mail + aliases are found in /etc/postfix/virtual:

user at domain.tld      user
alias at domain.tld       user

The matching could probably be done using a hook that scans this file.

Is anybody using a hack already to do the matching this way?
Perhaps somebody knows a less complicated approach?