Howto query (normal) users in Active Directory?

Hi,

I use the following domain path and filter to query the users in a domain in Active Directory (using C#):

dn:"DC=mydomain,DC=com"
filter:"(&(objectClass=user)(objectCategory=person)(company=myCompany))"

This works so far and returns a list of users, which is almost correct.

The problem is that this list not only contains normal users, but also functional email accounts such as "development@mycompany.com".

How do I have to modify the search criteria, so that those entries are not returned in the result?

Thank you

Magnus