Extending IMAP daemon to comply with legacy Proxy

[Thorsten Hater]

Hello,

I am currently investigating if and how to migrate a legacy setup based
on a modified Courier installation to Dovecot. So far I am really liking
Dovecot. however, I will have to work with an existing  IMAP  proxy for the
time being.

In particular, the proxy authenticates the user and looks up the location
of the mail directory and transfers the data to the actual server via an
extension of the IMAP protocol. This extension will have to stay and the
information transferred is not easily recoverable. Further database lookups
on the real server would be possible to solve the issue, but I would prefer
to keep the design intact at least for now.

Is it possible to handle IMAP commands after LOGIN/AUTHENTICATE
but before opening any mailboxes? Basically these commands aim to replace
the userdb lookup. Any pointers on how to implement this, perhaps as a
plugin?

Best regards,
  Thorsten