I run a basic forums site that requires activation by email, however, about half of the accounts (I'm not that popular of a site (yet)) return with Mail Delivery Failed errors (in response to the automatic email sent by the forums). The message details that the mail server sending the mail (IP 18.104.22.168 - FriHost's mail server IP I take it) has been blocked due to suspicions of spam. The has only occurred with mail.ru and comcast.net, and I have already taken matters into my own hands to remove this IP from their blocklists. Just thought I'd let FriHost know this. I'm guessing that some FriHost users are using email services for spam and that's why the server was blocked. So I don't know if you can do something about it or what... just letting you know.