Issues with Hotmail?

We are having a specific issue with Hotmail that seems to be caused by
Squid. The actual problem with Hotmail is that when composing a
message and Rich Text formatting is selected, then there seems to be
big delays in Hotmail displaying the icons on the page, and scripting
errors are displayed when the browser tries to load the HTML options
for composing an email. If Rich text is switched off then everything
works hunky dory. If it were up to me, I'd just tell the user not use
rich text, but other folks in our org insist it must work:-(

The reason I think it is something to do with Squid is that, using the
same PC and browser and bypassing Squid, the rich text option in
Hotmail works fine. Have tested with 2.3 stable 3 and 2.5 stable 5
with the same results.

Anyone have any ideas as to what could be happening please?

Relevant ACL config details are listed below, if they are helpful.
Basically we set rules so that our Opac machines can only access our
domain, with everything else allowed to anywhere else. There is no
specific mention of hotmail anywhere in our config. does there need to
be?

acl hertsd dstdomain .hertsdirect.org
acl opacs src "/usr/local/squid/etc/opacs"
acl libys src 10.0.0.0/8

http_access allow hertsd
http_access allow libys !opacs
never_direct allow libys
http_access deny all

Many Thanx,

Nig