Let's say we have two domains: contoso.com and fabrikam.com.

Both have:

  • two UPNs (.local and .com)


  • Contoso.com have Lync servers on-premise. Exchange, Sharepoint 2013 and Azure AD on Office365 (E1 licensing).

  • Fabrikam.com have AD and Exchange 2010 SP3 and Sharepoint 2010 on-premise. Lync on Office365 with logins synced through DirSync and authentication handled by AD FS (E2 lincensing).

Short-Term Objectives ordered by priority are:

  1. Handle GAL Sync,
  2. Share Calendars (including free/busy).
  3. Access Sharepoint's each others

Long-Term objective is disusing and remove Fabrikam.com.

Questions are:

  1. Without forest trust, is this mission impossible ?
  2. How to handle each on short-terms goal without complicating long-term objective ?
  3. How to make testing scenarios with hybrid deployement?



In my opinion, GAL sync and Calendar sharing should be accomplished via Exchange federation. I think this best nails down your 2nd question from both the "ease of setup" and "ease of teardown" requirements.

I'm afraid I am ill equipped to answer on the SharePoint Online side. SPO-SPO should be doable, but interacting with a on-premise environment and another org in SPO could run afoul of licensing?

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