Add warning / Port Choice and TorBirdy
It would be great if a note on port choice, when using TorBirdy with your email program could be added to the "Before using TorBirdy" manual.
It may sound trivial to even mention port choice. For the "average" user though, it could be unclear that certain ports are less suitable for anonymous communication. As exit nodes block certain ports, poor port choice for outgoing mail can narrow down the number of available exits.
The addition could be something like: Port Choice and TorBirdy Exit nodes allow or refuse certain ports in order to minimize abuse. Your port choice for outgoing mail could indirectly narrow down the number of available exits to communicate with your mail service provider and hurt your anonymity. Good port choices for outgoing mail are: xyz.
And then list some ports for outgoing email on IMAP/POP servers, that work well with the Tor infrastructure.