Hello,
not sure what you mean by that. That site seems to be working fine for me.
you seriously own the domain "domain"?.... what the heck did that cost you?
OP is talking about alias before his domain name. Works with out "www" but not with same words. This is not MyBB related issue, you've to ask your host about it. But for record you've to change some options in your DNS.
lol I missed the obvious.
Yes it's a htaccess issue but can also be handled via cloudflare or your DNS.
Ideally you should adjust via your .htaccess rewrite code.