Acer mail works in one environment, not in another

I am using an Aspire One under Linpus since 2 weeks. Internet works fine at home, either on cable or via access point.HOwever Acer Mail consistently reports "Server not reachable, try later" when I fetchmails from my provider.
But when I take the small gadget to my office, connect it via cable or WLAN, AcerMail would contact my provider in seconds and collect the mails.
Our home network runs since years, providing internet for generations of Windows machines 95, Nt, ... Vista.

Any suggestions what can go wrong at one place, but works fine at another?
Thanks for hints
Reprobus