This is something for after the 1.0 release but I think it's important and I'm going to try to figure out how to make it happen. I'd like to see some way to pass outgoing email from Thunderbird back to dovecot through some new command that we would have to make up. Email would be sent back over the IMAP connection and when Dovecot gets it dovecot would hand it off to an SMTP server that would deliver it.
If a crude experimental spec can be written I'll try to find someone on the Thunderbird side to write some sort of module to talk to it.
The reason for this is that I think that the elimination of SMTP from the client is a big step to control spam. The idea being that if IMAP can transfer outgoing mail the SMTP wouldn't be necessary for clients and we can block port 25 on windows machines and viruses can't send email. And the virus wouldn't have access to the IMAP password so viruses can't authenticate to send mail.
So - the key question is - what would it take to create an outgoing spec for sending email over IMAP? Like to see something clean and simple.