My 9front server sends and receives mail to and from the Internet, as well as accepting IMAP and SMTP connections over TLS from various clients, including Android, iOS, UNIX, and 9front itself. Excerpts from the live environment below.
Note: An “Inferno/POP secret” is used as the password for both IMAP and SMTP, which must be configured in addition to the user’s regular auth password. See: http://fqa.9front.org/fqa7.html#7.4.2
From /cfg/$sysname/cpustart:
cat /sys/lib/tls/acmed/stanleylieber.com.key >>/mnt/factotum/ctl
auth/as upas aux/listen -p 128 -t /cfg/$sysname/service.upas