It took ~48 hours because of very slow IO, but we are back on the most recent OS version. Happy day.
Mail delivery (SMTP).
Mail relaying by SMTP auth. (At last! Use mail.artifex.org, port 587 as your outgoing mail, require TLS, and supply your username and password – and you can finally send mail without relying on a gmail account.)
Mail retrieval (IMAP and POP, though POP’s not automatically tested.)
Spam filtering. (Spam goes into spam/, no user configuration or bogofilter required.)
This website (HTTP & HTTPS).
SSH for standard user accounts.
Probably nothing. But if you have a problem, please reach out to hblanks.