On Mon, 25 Oct 2021, Ron Garret wrote:
Note that message-ids are not guaranteed to be unique. During my test I found groups of as many as 20 different messages with the same message ID. (Turns out this makes quite a reliable spam signal!)
It's by far not a rare situation: duplicate message-ids happen whenever the sender names more than one local recipient during SMTP. It's a wholly unreliable way to indicates spaminess. However, if a high proportion of those recipients do not exist, ... Joseph Tam <jtam.h...@gmail.com>
