I've just discovered that the activation mails got rejected by web.de, because it thinks that the IP-address of the server is dynamic, what potentially can be used by spammers.
I logged a case for web.de. Let's see what happens.
Same problem:
gmx.net
gmx.com
myself.com
fantasymail.de
email.com
This is the same company behind, so no wonder.
I think I know what needs to be done. Experimenting now, but everything DNS related takes DNS TTL time 😁
Those who do not receive the activation mail - please send me a mail (see the Contact) with your username and your e-mail, and I will activate your account manually.
I hope I can do the next DNS change tomorrow. I wonder if it's the "not resolved" TTL or the usual one...
Another change:
"Reverse DNS changed. Please allow up to 24 hours for changes to take effect."
Still temporary, but it should fix the mail delivery for the time being.
The workaround works! I see the mail was delivered to myself.com and fantasymail.de!