Keep Thunderbird off. Quickly log into your webmail and see of 'drafts' exists online and has that message. Also check deleted/trash/bin in the online email. If you find it, open, edit and send it to yourself from webmail. If you can't retrieve it that way, please give more details - are you using IMAP or POP? Have you tried to 'search' in Thunderbird for that message in case it's moved or archived? Then if none of that works, what method of backup do you use and was the last one done while that message was in Drafts.

I searched my webmail (gmail). I could not find it. I'm using IMAP, but I don't know why or what that means. I've certainly searched Thunderbird in all my accounts. I'm on a Mac. I use Time Machine and back up to an external hard drive. And, yes, that message was in the Drafts folder for many back-ups, including the latest within the last month. That is what has lead me to ask you if I can somehow open an older saved version of Thunderbird and recover that unsent message. Or even if I could open just an old drafts folder and use a text app to get the list that is in the missing unsent message. It's not even much text, but it is nearly irreplaceable. Thanks for your help.

Hi IMAP means Thunderbird shows you what's on the Gmail server and syncs with it - so all actions in either Gmail or Thunderbird are mirrored in both. (The alternative POP - downloads messages to your local Thunderbird and removes them from Gmail.) However Thunderbird has local folders as well so you might have some messages saved only on your computer in Local Folders, and some in the Gmail account folder structure synced. I can't help with Mac and Time Machine I'm afraid... May I suggest you edit the original question to say it's Mac and Time Machine - or ask a Mac forum about extracting from backups. The other part you may need to add or ask as a new question is how to extract text of an individual email from a profile (once you have it recovered from backup). One more tip - Drafts are meant to be temporary storage of unfinished emails and might be tidied up by Gmail or other meddlesome processes. Use Templates to keep a message long term.