Third-party mail migration to Office 365 -- fixes and tips

John Speare, Senior Technical Writer, Microsoft

This wiki post has fixes and tips to help you migrate from third-party email solutions to Microsoft Office 365.

Third-party migration resources

If you plan to migrate an enterprise-level Google Apps solution to Office 365, you may be able to use the IMAP migration tool to move your email. But more complex user identity and document management migrations may benefit from the help of third-party companies that specialize in migration. We’re not making any recommendations, but here are a few of those companies:

  • Binary Tree provides cross-platform messaging migration and coexistence software with products that provide for the analysis of, and the coexistence and migration between, on-premises and online enterprise messaging and collaboration environments based on IBM Lotus Notes, Lotus Domino Mail, Microsoft Exchange Server, and Microsoft SharePoint.
  • Cemaphore provides migration solutions from on-premises Exchange Server to Office 365.
  • Quest Software provides migration solutions for Exchange Online and Microsoft SharePoint Online, including migrations from Lotus Notes and Novell GroupWise to Exchange Online.
  • Metalogix provides migration solutions to Exchange Online and SharePoint Online.

Third-party migration fixes and tips


I’ve migrated a portion of my Lotus Notes users to the cloud. My on-premises users are getting the dreaded winmail.dat attachment. How do I fix this?


Specify your on-premises (Lotus Notes) domain as a remote domain in Exchange Online. You must then configure the remote domain to disable Transport Neutral Encapsulation Format (TNEF) for all email that is sent to that domain.


Want to learn more? See Manage TNEF Message Formatting with Remote Domains.


Tips for Global Address List (GAL) sharing:

  • You’ll need Active Directory directory services provisioning. You can build your own management agent for Forefront Identity Manager 2010 or find a third-party solution. Most third-party messaging migration tools provide a solution for directory provisioning.
  • Use the Directory Synchronization tool to build and maintain Office 365.


Tips for mailboxes that have not been migrated don’t appear in the Exchange Online global address list (GAL):

  • When sharing the GAL between an existing third-party messaging solution and Office 365, it’s important that you configure a targetAddress attribute in the on-premises Active Directory users’ objects. The targetAddress value could be populated with the primary SMTP address or user principal name (UPN) for the user.


The format for this attribute is SMTP:emailAddress; for example,

  • You will need to deploy an Exchange Server schema in your on-premises Active Directory. This gives you the extensive mail-related attributes that the Exchange Server schema extension provides, such as targetAddress, msExchHideFromAddressLists, and other commonly synchronized attributes that are used in staged migrations.

Related content

Directory synchronization and source of authority

Cutover Exchange Migration and Single Sign-On

Simple Domain Sharing for SMTP Email Addresses