For years I have been a member of AMD Processor Forum (forums.amd.com), registered with a neverbox address. Recently the forums were migrated to FuseTalk bbs software, and members were supposedly sent new passwords via email. I never got mine. I tried their forgotten password feature but still no email. I tried setting up new user accounts using new spamgourmet addresses, but still no password emails.
Trying to imagine every pitfall possible, I took "amd" out of the address, shortened to xxx.xxxxxxxxxx@domain.tld format, and switched to mamber.net. None of this worked.
Finally I registered with a non-sg account in the format xxxxxxxxxx@domain.tld, and it worked.
I can only conclude that their software doesn't like periods anywhere before the @, or doesn't accept spamgourmet addresses. Either way, that rules out using spamgourmet. (Well, I haven't tried a ~ yet.)
I will try to find out which it is.
I would not suggest contacting them yet, since the migration went badly in several other respects, and they are up to their butts in alligators right now. I'll keep you posted.