One of my alias doesn't work

Hi,
I try to get a letsencrypt cert for one of my alias. The ipfire is running on an esxi 6.5, he has the ip xxx.yy.224.87, the server has the ip y.x.174.94. Normaly everything working with the routing, I’m reaching the server. But when the acme service ist starting, I get this log entries:

Initializing, please wait...
Using existing domain rsa key /var/lib/acme/acme/key.pem
Using existing Lets Encrypt account key /var/lib/acme/acme/account.pem
Detecting IP addresses...
OK: xxx.yy.224.87
Found A record for autodiscover.xxxxx-yyyyyyyy.de: y.x.174.94
Cannot match your IP xxx.yy.224.87 against hostname autodiscover.xxxxx-yyyyyyyy.de (DNS returned y.x.174.94)
Found A record for autoconfig.xxxxx-yyyyyyyy.de: y.x.174.94
Cannot match your IP xxx.yy.224.87 against hostname autoconfig.xxxxx-yyyyyyyy.de (DNS returned y.x.174.94)
Found A record for mail2.xxxxx-yyyyyyyy.de: y.x.174.94
Cannot match your IP xxx.yy.224.87 against hostname mail2.xxxxx-yyyyyyyy.de (DNS returned y.x.174.94)
Cannot validate any hostnames, skipping Let's Encrypt for 1 hour.

Why ipfire doesn’t route normal traffic to the right server, and the acme traffic not?

Regards Bernd

Do you have the guess my ip with external servers checked.

The DNS ist OK, an nslookup gives in both directions, forward and reverse, the right answers

Regards Bernd