Belkin Router Outlook problem

If I download my emails through the Internet-no problems, If I use Outlook (or express) I only get the odd email. This problem only started when I changed from a normal ADSL modem to a Belkin Wireless Router/Modem, the problem exists whether I connect Wirelessly or by cable to the router. Everything else (Internet) appears to work ok. Are there any Router settings I can play with?