bbs.spamgourmet.com

Suppose someone registers a domain name, and then points the MX record of that domain to SG's mailserver. Then suppose mail is sent to mykeyword.myusername@mydomain.tld. Will that work? Or will SG reject it because the domain name is unrecognized?

The message will be rejected -- let us know and we can set it up on this side, though.