Forums think my IP address is spam

When I have tried to join a couple of forums in the last few years and when I go through the registration process I get an email notification that I have been banned for spam. I was able to contact one forum administrator and was eventually allowed but the second forum will not respond.

This is very annoying as I use forums as a source of reference to educate myself on hobby project.

In the past forums were extremely plentiful but lately a lot of smaller forums have ended and only larger more dominant forums continue. There are fewer options and now I seem to be excluded from them.

The first time it happened the administrator said it was something to do with my IP address. I don’t remember exactly what they said it was. I just remember it was something related to spam. Is there a way to clear my ip of this?