Looking at the problems Mail3 has had, which affected a client of mine, and I see Tanmaya mentioned some “POP3 abuse” going on.
Just so I can tell clients, and as a guide for myself, what exactly is POP3 abuse? Does he mean something like a cron job checking a POP3 mailbox too often or something like that? I thought it would have been smtp abuse…?
There was a client’s POP3 check scripts that were not exiting or closing connection. Next there were a few IPs that tried to open many many POP connections to the server, probably testing some kind of software, if not intentional abuse. Since this was all fetching data at the same time and none was ready to quit, it caused much of I/O wait and hence the issue.