Why is my server on a blacklist. It's not uncommon for a mail IP address to end up on a public blacklist, especially on a shared server. It could be due to overall volume of mail coming from that server, or messages seem to have characteristics of spam in them.Another common cause is email forwarders.s such there are public blacklists of mail servers that have been relaying spam. This allows other mail servers to check if an email is from a server's IP address that might have possibly been flagged for sending spam in the past.