I did a quick back to mutt after 2 or 3 years of uninterrupted thunderbird usage, the main reason was I was tired of waiting on thunderbird to sync the sent and draft folders. What I love of mutt is not mutt itself, but offlineimap or even better isync which is faster and uses less resources.
after a few days running mutt I found I wasn't being productive as I used to be, using mutt made me slower. that was sad. :(
Then I realized I could save to sent folder delivering to myemail+sent@mydomain, and thunderbird does support that. I became happy again :)
I had a few annoyances, like renaming my folders from Drafts, Sent, Trash and Junk to drafts, sent, trash, and junk but this extension and doveadm mailbox command were really helpful.
EDIT 2015-12-30, I went back to mutt in November.