Starting...just now, whenever I try to send an e-mail via the web interface, I get the following error message:

There was an error sending your message: sendmail: service unavailable (69)

Happened repeatedly, on same and different messages. Never seen anything like this before.

Best contact JT:
support[at]spamcop.net, or click the "Problem" button on the top menu bar when logged in.
Appreciate an update, if you could, on how it turns out.

Server went down / service quit running.

Apparently, it didn't last long enough to be newsworthy. It could well have been a server undergoing maintenance / reboot at the time you were trying to send your e-mail.

Also noting that hti sis the only post in the Forum, nothing in the newsgroups, so it wasn't down for long apparently. Anyway, a test e-mail just now worked just fine.