EHLO 127.0.0.1 is not a good choice
Torbirdy uses 127.0.0.1 to identify itself when sending mail. Unfortunately this value is also commonly used by spammers and so a sensible MTA config will reject connections identifying themselves like this.
Using tor to send mail already identifies the sender as using tor, obviously, because the exit gateway will be known/identifiable. Therefore fingerprinting on this value should not be a concern.
Propose to change this to a valid hostname, which should be created in the DNS, such as,
birdy.torproject.org. IN A 127.0.0.1