Hi,

I started out with creating a ticket on the Mojang website were I've been told that they can only deal with account and billing related issues. They refered to this bug tracker.

I'll just resend my support request/possible bug here:
"We're currently having issues with a customer IDN domain that contains "ü".
The gameserver is running on port 25576, which we added to the SRV record for the main domain. When trying to connect to the server with the domain in Minecraft, it does not work. However, when we try it with the domain followed by the port (:25576), it works. This seems to be a problem with our SRV record at first, but interestingly enough  **connecting to the server with the ACE format (xn--...) of the IDN domain without specifing the port works. So I think that our SRV record is in fact fine.

Quick overview:
xyzü.de: Does not work
xyzü.de:25576: Works
xn--...(Domain in ACE format without port): Works

SRV record: https://imgur.com/a/8u3oo2W"

Is it possible that this is a problem on your end?
I successfully copied the DNS settings to a non-IDN testing domain and it understood the non-standard port with help of the SRV record without a problem. On top of that, I read about servers that use IDN domains. It might be possible that they are using the standard port, which is why they don't have to rely on a SRV record.

Update:

As I'm currently on holiday, a co-worker of mine did take another look at this issue in the meantime. He took a look at the DNS requests Minecraft is issuing via Wireshark, which I should have done aswell actually.
Minecraft is looking for SRV records for the domain with the "ü", so for example

_minecraft._tcp.xyzü.de

The ü is actually \374 in this case, but it is the same issue. Shouldn't it look for SRV records for

_minecraft._tcp.xn--xyz-joa.de

?

Similar issue: MC-11651
It would be interesting to know if the tester of the fix used a server with a standard port.

Thanks in advance and best regards,
Paul