I have Icewarp EMail Server and there is a Lets Encrypt cert created long ago. Many times I have renewed or created a new certs without problems in Icewarp administration console. But today I can't. Error is: Error when registering acme account. ACME Exception: Error registering: 405 HTTP/1.1 405 Not Allowed
Sorry for my English.
My domain is: mail.zeinet.kz
My web server is: Icewarp Email Server 126.96.36.199
The operating system my web server runs on is: Windows Server 2012 R2
That's HIGHLY unlikely. There currently is no incident at https://letsencrypt.status.io/ and I don't see an sudden influx of new threads with the same kind of issue. Further more, it isn't even clear what your issue actually is? The error "ACME Exception: Error registering: 405 HTTP/1.1 405 Not Allowed" is not a literal error presented by the Let's Encrypt ACME server, so I have no idea what the actual error is. Could you perhaps show us more of the error? Perhaps from a log file in Icewarp?
If it was working as of a few months ago and isn't now, then it's probably due the removal of the old ACMEv1 endpoint.
It had been only allowing renewals for existing names for a long time to let people upgrade, but has finally gone away for good.
If that's the case, the only solution is to upgrade your client to a system that's uses the updated endpoint. If it's integrated with your software, you probably just need to upgrade your software to a version from within the past few years.
I think also the POST-as-GET change was enforced recently, I could be wrong. That meant that any old acme client that tried to use and http get to fetch one of the resources would fail until it changed to using an HTTP post. So you could be more or less acme v2 compatible but still fail.