If you're on .NET 3.5 (or you can upgrade to it), you can use the new System.DirectoryServices.AccountManagement
namespace to make this quite easy.
Read more on that new .NET 3.5 gem here: Managing Directory Security Principals in the .NET Framework 3.5
// create a context - you need to supply your
// domain NetBIOS-style, e.g. "CONTOSO"
PrincipalContext ctx = new PrincipalContext(ContextType.Domain, "YOURDOMAIN");
// find the group you're interested in
GroupPrincipal gp = GroupPrincipal.FindByIdentity(ctx, "YourGroupName");
// enumerate the members of that group
// the "true" in GetMembers() means: enumerate recursively, e.g.
// if another group is found as member, its members are enumerated
PrincipalSearchResult<Principal> members = gp.GetMembers(true);
// iterate over the principals found
foreach(Principal p in members)
{
// test to see if it's a UserPrincipal
UserPrincipal up = (p as UserPrincipal);
if (up != null)
{
// if it is - set the new e-mail address
up.EmailAddress = "[email protected]";
up.Save();
}
}