Now and then, when people register in the forums or sign up for membership, they're using email providers that send a message back to me that reads something like:

"Your email with subject Registration at Online Alano Club Discussion Forums ( From Online Alano Club Discussion Forums ) has been blocked because your email address Online Alano Club Discussion Forums is not recognized as a regular correspondent."

And then I'm supposed to reply, and get registered with their system, etc.

I don't do that. I will not do that. You will not get registered if your email system sends such silly messages to me.

Get a real email provider.