There seems to be a strange limitation in your forum signup process.
I tried to signup with the email address I used to buy my license, but the verification email never arrived (two attempts.)
I changed to a @live.com email address and that arrived immediately.
My purchase email ends with .us and that might be the problem. I’ve had that problem before.
(No, the verification email is NOT in my junk mail folder.)
Joschka
We just use Discourse.org for our forum software, nothing unusual. I will see if I can find something on my end and I apologize for the issue.
I updated my question to add that the verification message is NOT in my spam folder. I check those regularly.
Sorry, I had updated mine to remove that part about spam too after re-reading yours. 
It was not wrong to ask and I’m not offended.
this is really strange. I had no problems with it at all
There are some systems that use outdated rules for validating email addresses. I have encountered a few that falsely reject @xxx.us email addresses, such as my main one.
As I recall, Discourse.org is one of the offenders.
That may be what this problem is all about.
Jam