MacMail very slow connecting to server

I have a persistent problem with downloading and sending e-mail through my university's pop server using Macmail. I've been in consultation with staff at the University and my ISP, and they don't have any solutions to this problem. Below is a general description of the problem that I'm having. Wondering whether anyone has any ideas...

A couple of months ago, suddenly and for no reason I can determine, response speeds from the University pop server dropped off dramatically. The problem seems to be the time it takes for MacMail to log onto the popserver. Typically it will take 60-90 seconds to log on (monitoring this through the Activity window), and then everything proceeds properly. I'm using MacMail on my laptop (MacBook, OSX 10.5.8). Normally I use a wireless connection. I've reset the modem and the wireless router numerous times. The same problem is there when I use the ethernet cable directly into the computer from the DSL modem (by-passing the wireless router). Normally in the past when I got or sent mail, the response was virtually instantaneous, with a little lag for download times. If I got a big attachment, it took a little longer. I tried restarting MacMail, restarting the computer, etc., and none of this changed anything.

It seems that I can always get access to mail using the pop server, but it seems to take forever for MacMail to log on to the server and accomplish the task.

For a while (actually, quite a long while) I had problems with download speeds at my house. I'm on a DSL through a local company. When things were working right I got upload/download speeds of 0.31/1.31 mps, typically. Sometimes it dropped off a bit, particularly for download speeds, which would become about 0.81mps, instead of the standard 1.31 mps. (This as measured by Speakeasy.) However, when this pop server issue emerged, I decided to work on the speed problem. Finally my ATT repairman found an ants' nest in one of my main phone relays. After cleaning that out, and reconnecting all the wires, my dowload/upload speeds have been consistent and reliable (0.31/1.31mps). Nevertheless, the MacMail problem persists.

I can also access my e-mail account (through the University) over G-Mail (google apps). When I use GMail, things work fine. Speeds are good. Also, everything seems to be OK through the webrowser in other applications (e.g., Firefox).

Here's the real wrinkle: Whenever I use MacMail elswhere from the same laptop, it seems to work fine. From my office on campus, whether using the wireless network or using an ethernet cable, I get immediate response from the popserver. And, I've also tested from a friend's house. She also has a DSL, her DSL connection from the same ISP that gives exactly the same download/upload speeds. When I use MacMail from her house it works fine. But from my house, it typically takes 60-90 seconds for MacMail to log onto the popserver, and then to begin sending/getting messages. (Again, this was a check with my same laptop, using wireless connection in both locations.) And, recently, on a trip to Asia, MacMail also worked fine: from Bangkok and Sri Lanka. Why my computer would experience problems only with MacMail, and only from my house, is a mystery to me.

So, I have no idea what's going on. None of my tech resources locally has any idea. Does anybody have a suggestion?