If your synced contacts appear in the GAL, but the attempt to old emails fails, you may need to set legacyexchangedn on the Synced contacts.  This may be necessary on any version of Exchange 200x, including Exchange 2007.

To do this, we suggest you manually create an object in the target destination OU.  Then, in ADSI edit, look up the legacyexchangedn value of that manually created object.  For example, it may look like this:

/o=First Organization/ou=Exchange Administrative Group/cn=Recipients/cn=John.Smith

Then, again using ADSI Edit, manually set the legacyexchangedn of a problem synced contact.  Attempt a Reply To mail test.  If the test is successful, you have confirmed this format is valid and should fix your problem when applied across all synced contacts.  This customization can be applied via a custom legacyexchangedn mapping.

If you do not already have one, create a Custom Map file for this connection. Using the legacyexchangedn format you obtained from the manually created object, add a new custom mapping definition for legacyexchangedn.  The final component  of the legacyexchangedn value needs to be customized to contain a variable. The below example uses ~smtpname~.~smtphost~.  This is the same value as is used to set the destination alias (mailnickname) on a sync created contact.

For example:

legacyExchangeDN=/o=First Organization/ou=Exchange Administrative Group/cn=Recipients/cn=~smtpname~.~smtphost~

(The legacyExchangeDN mapping should appear in the map file as one long line.)

Click Save to save the customizations.

Click Apply to save the custom file name.

Run the Sync.  You should expect to see Modifies occur on all objects.

Perform a Reply To test to verify desired results.