Google Apps Mail link always opens an unrelated domain

I'm using Mac OS X 10.5.3 and running Firefox 3.0 (rv 1.9) (although
this problem has travelled with me through Firefox 2, Safari and
Flock)

Each time I click on an email address within a message in my own
domain (to initiate a new message) I am redirected to

https://www.google.com/a/shimer.edu/S...

Which is a domain that I have no connection to.

Consequently I have to

copy the mail address,

open 'create new message'

and manually and paste the address into my message.

Surely things can work better than that :-)

Any help would be surely appreciated.