The Exchange RUS and external AD contacts

One thing that the Exchange 2003 SDK does not warn you about when adding mail enabled external Active Directory contacts is the Exchange Recipient Update Service (RUS), and this will cause strange effects when Exchange tries to resolve mail addresses. I.e. you will not be able to send e-mail to external mail contacts. Note that these effects will not happen immediately due to the periodical processing schedule of the RUS, thus you can test and believe that your code is correct, only to get hit in the face a few hours later.

The problem is that even if you set only a SMTP mail address on the new AD contact as shown in the SDK, the RUS will apply all the other types of mail addresses defined in your Exchange policies during its processing. This will give the external contact an internal Exhcange address, an X.400 address, etc. Thus, Exhcange will not be able to resolve or deliver e-mails to these contacts as most of these addresses will be bogus.

To correctly mail enable an external AD contact you need to set a GUID in two specific Exchange properties on the AD contact:

DirectoryEntry adContact = adContainter.Children.Find("CN=" + contactId, CONST.AD_CONTACT);

//exlude from RUS
adContact.Properties["msExchPoliciesExcluded"].Value = "{26491CFC-9E50-4857-861B-0CB8DF22B5D7}";
adContact.Properties["msExchPoliciesIncluded"].Value = "{26491CFC-9E50-4857-861B-0CB8DF22B5D7}";

//set mail AD property to e-mail address
//must set again after exluding from RUS
adContact.Properties["mail"].Value = mailAddress;

// Write Exchange information to the directory.
adContact.CommitChanges();

The policy GUID must be set on both the Exchange RUS policies excluded list and the policies included list. The specified GUID is valid for Exchange Server 2003. Refer to my previous post for details about how to write code for Exchange Server 2003.

You should also ensure that you never add an internal user's mail address as an AD contact through code. If your code does not prevent this, it will prevent Exchange from delivering incoming e-mail to the user's mailbox as it cannot resolve the mailbox when both an AD user and an AD contact has the same address.

Note that you should not exclude mail enabled AD distribution group (mailing lists) from the RUS, as this will cause the mailing lists to stop working. They must be processed by the RUS to function properly.