Users moved to #office365 Exchange Online but on-prem GAL affected

In a recently upgraded hybrid 2010/2013 environment with Single Sign On there can be a problem with the on-premises Global Address List.

Below is how the issue manifests itself for users and what can highlight the issue;

  • As soon as a user is migrated to Office 365 it no longer exists in the on-premises GAL for on-premise users.
  • GAL for the migrated user works fine, it shows both on-premises and O365 mailboxes.

Firstly it would be wise to check the following location in the Exchange Management Console – on-premise

exchmanconsoleYou need to check whether the migrated mailboxes are shown as ‘Remote Mailboxes’ as shown in the screenshot under Recipient Type Detail.


The solution for this is to check for any instances of a ‘custom GAL’ – if this is the case then you will need to remove this custom instance as it doesn’t allow on-premise and Office365 to correctly populate the on-premise Global Address List.

About apoth0r
IT Professional and Cloud Evangelist! & Streamer! Managed Services | Solutions | Procurement | Support Services | Cloud | Fujitsu

2 Responses to Users moved to #office365 Exchange Online but on-prem GAL affected

  1. Arndt says:

    This might be the solution!
    Do you know how to determine a “custom GAL” in Exchange 2013?
    Running Ex13 in Hybrid mode, getting the same results as described under your issues.

    • A custom GAL will be anything other than the default – so one that has been created outside of the normal/default GAL. To determine you need to see whether you have a default alongside your created within Exchange Management Console

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