Post your error messages and codes or at least the name of your ISP
so someone can advise you on the set up.
Also... If you are a Norton or McAfee AV victim give serious
consideration to replacing them with free Vista compatible
products such as Avast or AVG because they will bite you
eventually even if they are not involved in your current problems.
Email scanning should be turned off in any anti-virus. Also exclude EML
files from the scan. It provides no
protection not provided by the regular resident protection.
Besides that, McAfee and Norton are not compatible with Windows Mail and
should be uninstalled.
If that doesn't fix it post the exact error message.