I just got this error while attempting to provision Exchange 2007 users with ILM 2007 FP1:
Event Type: Error Event Source: MIIServer Event Category: Server Event ID: 6801 Date: 15.09.2009 Time: 10:14:02 User: N/A Computer: ILMSERVER Description: The extensible extension returned an unsupported error in MIIS. The stack trace is: "Microsoft.MetadirectoryServices.ExtensionException: **** ERROR **** ExternalEmailAddress is mandatory on MailUser. **** END ERROR **** **** ERROR **** The mail contact and mail user must have a valid external e-mail address. **** END ERROR **** at Exch2007Extension.Exch2007ExtensionClass.AfterExportEntryToCd(Byte origAnchor, String origDN, String origDeltaEntryXml, Byte newAnchor, String newDN, String failedDeltaEntryXml, String errorMessage) Microsoft Identity Integration Server 3.3.0118.0"
This event had been asked about on the Technet forum, but the answers talked about rollup versions – and I had RU9 on both the Exchange and ILM servers.
Eventually I figured out there was a typo in my homeMDB string. The clue was that all the expected mail attributes were populated in AD, except homeMDB.
Now what “ExternalEmailAddress” has to do with homeDMB I do not know!