new internet provider, now mail won't work

I recently moved to a new city and have switched from Sympatico as my internet provider, to Eastlink. Since the switch I cannot send mail from the Mail program.
Neither one of my email accounts is a sympatico based account (one is gmail, one is a work address with a smaller provider), but I'm wondering if the switch could be the issue since I've never had problems before. I have run a connection doctor and the only account the comes up with a problem is the W3 Connex service provider, both the gmail outgoing and incoming mail server claimed to be working fine (but still I cannot send msg with this address).
Do I need to set up my SMPT server to correspond with my new service provider or with the email providers? This is really frustrating as I cannot send anything with my work address and have to log on to Gmail's web page to send anything with that address...
What the **** is going on?