Message sending stopped working since feb 4

Hi guys,

My SMTP server stopped working 4 days ago. It marks messages as sent but I receive server notices 24, 48 and 72 hours after… not delivered but trying, then fails. I didn’t change anything.
I use K9 on Android,TB on mac and round cube on the web. All fail.
I was prompted to install s/mime some time back but even deactivating encryption nothing works.
I know its not k9, but my ticket with my ISP doesn’t receive any response…
So if someone has an idea were to look?
it would be appreciated.

Which mail provider? Which version of K-9?

As you indicate, this is happening regardless of your mail client and not a K9 issue. Rather it’s a problem that your mail service provider is having.

If all your messages, to addresses at a range of domains, are being returned then the issue could be that your provider is on a block list so not able to connect to deliver your messages. If it’s only messages to a couple of domains, but others are getting delivered, then it could be that those target mail servers are unreachable for some reason, including being down or your provider being on a more limited type of block list. The warning and returned messages you are getting may provide some hints, but not always.

In the end, this is an issue that can only be resolved by your mail service provider - or moving to a different provider.