Had someone I talked to who used a recycle bin utility (Fundelete). With IMON, it slowed down his incoming email to a crawl. . . He was using Thunderbird and Eudora. With IMON turned off incoming email went back to normal. They tried changing the compatiability slider in IMON but that didnt help. . . Thought i should say something in case other people ran into this problem. They uninstalled Fundelete and it solved the problem.
Since Fundelete serves to store a copy of each deleted file in the recycle bin, I assume they must have received a larger archive (or simply a bunch of worms) whilst IMON attempted to unpack the archive(s) first. During this process, IMON created temporary files, which might have caused the system to slow down due to fundelete putting copies of those temp files into the recycle bin.