[9front] AUTHENTICATE failed can't get challenge (imap4d)

[sirjofri <sirjofri+ml-9front@sirjofri.de>]

Hey all,

for a few days now my mobile mail client (FairEmail) receives the message "AUTHENTICATE failed can't get challenge" together with log messages about failed SSL handshakes and connection resets by the server.

The server is a 9front server. I never had any issues like that, and I also didn't change a thing recently. The only thing I did was running acmed to update the certificate for https (imap4d uses another cert iirc, which I manually checked in my mail client: it isn't signed by a CA).

Surprisingly, my mail client still works as expected. It's just the notification popping up every now and then, and it can't connect at that point, but a few minutes later it works fine. I can also receive and send mail (like this one).

Does someone know what could cause this?

I didn't investigate further yet, as I didn't have the time, but if someone has a hint I'd be happy.

Have a nice day

sirjofri