With the following,
(printf '* OK [CAPABILITY IMAP4rev2 AUTH=PLAIN] test\r\n' | nc -l -p 1234 > /tmp/log) & aerc
[local]
source = imap+insecure://me%40example.org:test@127.0.0.1:1234
default = INBOX
from = Runxi Yu <me@example.org>
I see LOGIN instead of PLAIN. LOGIN is kinda deprecated. I was able to
reproduce this in add9e15e475d8e22d7ed1452ced37d7ec7ff8aff and 0.18.2.