I'm using the mail module of nginx to proxy and loadbalance IMAP+POP3 connections to backend servers. I do authentication via http authentication.
Some Clients are sending IMAP ID commands to the server with information about their software and version. I would like to log that and maybe use that during authentication. It would be great if nginx would support that command, and if it has been sent before LOGIN, also provide the information to the http authentication script. IMAP ID can be found in RFC 2971: http://www.faqs.org/rfcs/rfc2971.html
The information about the client could be used to route the user to a specific backend server that has some client-specific IMAP bug fixes in place, or could be used to restrict logins of a specific user to only one specific client if the user wants that for slightly higher security, or for a list of "last activity of the user" like GMail does, or just for client statistics.
I'm not a C programmer, so sadly I cannot write a patch myself for this, but maybe someone is able to add this small feature?