outlook 2003 not receiving email but able to send

Outlook 2003, XP Pro,  relatively new Dell, two identical Windows 2003 servers running active directory and sharing the load.  She can access the internet and send email, although she thinks some people may not be receiving her emails.  She cannot receive email.  She can access her email server by going to mail.hercompany.org, and doing web mail.  we can ping mail.hercompany.org as well.  All other applications appear to work OK.  Other people in her organization appear to work just fine, with similar settings.  Her tcpip is hard coded, using 192.168.2.xx/24, dg is 192.168.2.1.  Her DNS is set to server1, server2, 207.207.03, 4.2.2.1, and one other dns.  This setting works perfectly on other pcs in the area.  it does not work if you remove server1 and server 2, and does not appear to work if you reverse them in the dns settings.  i went to another pc which has working email, and logged in as her (new account setup), put in her email settings, and same problem.  her email provider claims that nothing is amiss; it all looks good from their end.  and, no one else in the organization is having this problem.  we are running through a sonicwall firewall, less than a year old with pretty recent firmware, then a cisco router and a fractional T1 (voice/data).