What version of FW is currently loaded?
What the MFr and model# of your ISP modem?
What is the Mfr and model# of your PC? Wired or wireless to the router?
Very odd, have never seen this issue, however I don't personally use Outlook, I use Thunderbird. I have one that works from home and they use Outlook, I don't know what version though.
This happen with other PCs loaded with Outlook?
Try loading Thunderbird and see if it does the same thing.
Possible you could have a bad unit, however odd that it only effects outlook mail.