Another one. Just noticed why I wasn’t getting any mail from forumosa. Mail is being rejected because it comes from host “oriented.forumosa.com”, but that host doesn’t exist:
% host 66.135.38.230
230.38.135.66.in-addr.arpa domain name pointer oriented.forumosa.com.
% host oriented.forumosa.com
Host oriented.forumosa.com not found: 3(NXDOMAIN)
Solution: add DNS record for oriented.forumosa.com with address 66.135.38.230.
The rule that rejects this kind of mail is standard on most mail systems these days, so probably lots of mail from forumosa is just being dropped.