.Mac mailbox is slooooow

[Kynan Shook]

OK, anybody have any bright ideas with the following problem?  I just 
recently merged the mail going to two different .Mac accounts to just 
one, and I have a set of rules to sort messages from certain senders 
into a folder to catch my attention better.  However, although the 
messages download and filter just fine, actually retrieving the message 
takes FOREVER.  Mail.app doesn't cache it right away like it seems to 
do with most other messages, and when I click on it to read it, it 
takes it forever to download the message.  Usually what I have to do is 
click on the message to get it to try and download the message, wait 30 
seconds or a minute, click off the message so it stops trying, and 
click the message again so it starts again; eventually it has actually 
downloaded the message, even though if you just click on it once it 
never stops "trying."  This happens on a 1.5 Mbps DSL connection, as 
well as at the university I work at and attend, so it's NOT a network 
speed or other network related issue.  It could be a computer issue, 
though everything else seems to be working fine in Mail.
Of course, the plain inbox works just fine.
I have rebuilt the mailbox, and it still happens.  One note from when I 
was rebuilding the mailbox; every 20 or 30 seconds, it would generate a 
lot of network traffic (sometimes 100 KBps+ for a second or three), and 
then it would sit doing essentially nothing for the next 20 or 30 
seconds.
Guesses?
Thanks,