Notmuch backend doesn't allow saving sent messages to the maildir. Gpg encryption produced an error when I tried it just now. Scripting is limited: actions that you can assign to keybindings can do only very simple actions (which might be a good thing if aerc finds just the right set of simple actions to make available).

Recently it was producing errors if the mime-type of an email attachment is quoted. This is something very rare, but some mailers do that. The issue was fixed within a couple of days after my report.