Blacklist / Blocklist

A list of IPs or domains flagged for sending spam. Being listed can block or filter your emails. Good sending practices help avoid it.

Some blocklists are managed by ISPs while other blocklists are operated independently and are sometimes referred to by ISPs to filter out bad actors.

It's important to note that not all blocklists carry weight in the decision-making of ISPs. Some blocklist operators even accept compensation to remove a sender from their list, even if that listing is not materially impacting deliverability. Not all blocklists are created equal!