Most likely you have a wiring problem (as the only change was replace a switch) in your building, with intermittent connection problems. This will affect software protocols that are poor in recovering from faults, like paradox databases and open imap connections. The only way to catch something like this, is to investigate piece by piece what is happening in each segment of your network.

Edit add: I should have said also, that with Vista you need to open explorer, and make sure explorer reconnects the drive, before you attempt to restart Pegasus Mail.

Recently I had a switch go bad.  I replaced the hardware and now I am getting all kinds of IMAP connections problems.  PMail will connect to Mercury and work fine for about an hour and then for no reason the connection fails.  The only way to get it going again is to close Pmail and restart.  These are all XP Pro boxes.  Any suggestions?

 Also, I have a Vista laptop that connects through IMAP and then all of a sudden disconnects.  But when I try to restart Pmail it won't connect at all.  I can't even access the mail server through network neighborhood.