A mind-boggling problem in MS Outlook

First of all; I'm from Iceland so you have to excuse my english.

I have an extremely interesting problem.

I have a laptop and I use Microsoft Outlook 2007 for email (pop3). I use this computer in three different locations, at my office, at school and at my home. All of these locations have, as you may expect, different outgoing mail servers.

So the problem is sending e-mail from my home. When I'm at work or school I have no problem sending and receiving mail, but when I'm at home I receive mail but the problem is sending.

At first, you would think that I typed in the wrong mail server but that's not the case. And everything looks right. I send the mail, it goes into the "Sent mail items" folder and I get no feedback about any errors. But the mail never reaches the recepient.

The strange thing is, that this only happens at my home.

I can't imagine anything being wrong with the e-mail account, because it works everywhere else.

Here's what I've tried:

I have set my account up on another computer at my home and it works like a charm.

I have checked with my email provider and he says there's nothing wrong with the account (given that it works everywhere else and also through the web interface)

I have put a new router in my home - nothing

I have re-installed MS Office on my computer - nothing

I set up another account up on my MS Office - mail doesn't reach the recepient through that account either.

And I've tried various other things that I don't bother to mention here....

I've also talked to many computer specialists here in Iceland and they have no answer.

That's why I'm looking "over seas" for an answer.

What could be the problem?
Is it the setup of Office on my computer?
Is it my computer (Lenovo ThinkPad R61)
Is it the internet provider at my home (I doubt it because it is the biggest provider in Iceland)
Is it my account?

Hoping for a reply

Olafur Bjornsson