Hi,
Using Thunderbird+Enigmail+Torbirdy.
To solve this the user need to manually set the account drafts settings (in Copies & Folders) to keep drafts on Local Folders.
I think Torbirdy should do it by default.
This info should be added to known issues on Torbirdy wiki.
(If I recall correctly, this issue was discussed before also but I can't seem to find the thread/ticket.)
By default, Enigmail saves an encrypted copy of the message. This is the default setting [1] and I think it also confirms this when it saves an encrypted message for the first time. TorBirdy does not modify this setting so it should be enabled by default for Enigmail.
If you did not change this setting but still observed this behavior, please open a bug report [2] with all the relevant information (version of Thunderbird, TorBirdy, Enigmail, etc.) so that I can check this.
Come to think of it, perhaps we should disable the automatic save feature altogether (#6337). Suggestions welcome.
[1] - https://www.enigmail.net/documentation/userprefs.php (see saveEncrypted) [2] - https://trac.torproject.org/projects/tor/wiki/torbirdy/dev