Tuesday, January 20, 2015

Did You Know: O365 Onboarding Changes #MSExchange #Office365

The latest Office 365 “What’s New” post introduced a change to the onboarding message size limits. The old limits of 25 MB have been increased to 150 MB while onboarding mailboxes to Office 365. This is great news and I know many customers will be very happy with this. Well, I know even more consultants that will be sleeping better at night with this increased flexibility!

The verbiage of the official announcement stated that:

                  Office 365 Exchange Online message size onboarding limit increase — We are making a change to allow customers to migrate larger mail messages to Exchange Online. We now allow messages up to 150MB to be migrated to the service. The change is available immediately to all customers and is published as a new limit in the Exchange Online limits page in the Office 365 service description. We are not changing other limits such as mailbox size or maximum send/receive limit for messages. This change enables customers with large messages to easily migrate their existing content to the message.

The service description reflecting the change has been updated as promised here. After the initial excitement of the announcement wore off many in the community, myself included, started to have questions around how this new change was being implemented. For instance, would the traditional third-party migration methods be allowed to take advantage of this increase? Some of these tools leverage EWS or IMAP to migrate data into O365. After some internal discussion with Microsoft they have clarified how the change will be implemented.

The following two statements are true:

1               The 150 MB onboarding change is only valid for native MRS-based moves and not for EWS, MAPI and IMAP. 
2               Any migration methods that rely on the mailbox already being created in O365 will be subject to the 25 MB limit.

The changes to the onboarding message size will only apply to moves that utilize MRS and users that are staged with an MEU RecipientType in hybrid configurations. Other third-party solutions that target UserMailbox will be subject to the traditional message limit, as MRS is not being called.  

Also, some have asked if any changes need to be made to the send connectors for hybrid mailbox moves. Since mailbox moves are a function of EWS via MRSProxy, they are not related to transport. The transport rules will not kick in because a mailbox needs to complete the migration before the mailbox plan is associated with it. Once you have a mailbox plan associated with a mailbox the transport limits will then be enforced.

Hopefully this helps to clarify the onboarding message size changes. Don't mind me as I start to smile while moving large attachments into O365!


  1. Hi Justin,
    Can you clarify what the 150MB limit for send/receive for EOP standalone customers actually means?
    If I configure aadsync to synchronize user accounts between on-premises Exchange and Exchange Online, but all mailboxes reside on-premises, will they be able to send/receive 150MB emails at a maximum? (obviously based on on-premises config as well).
    Then if their mailboxes are moved to Exchange Online, they are subject to 25MB limits? I just need clarification on when the 150MB limit applies.

  2. Hi Robert,

    The 150MB on boarding change does not increase the established O365 send/receive limits. The O365 send/receive limits, and Transport in general, does not come into play with this change.

    You will be able to migrate mailboxes that contain attachments up to 150MB in total size to O365 if you are running in a hybrid setup and using aadsync to create MEU objects in O365.

    This means when you perform a New-MoveRequest to migrate on-premises users to O365 these mailboxes can contain large attachments.

    Prior to this change, when you performed a New-MoveRequest for a mailbox that had attachments larger than 25MB the move would skip the large attachment.

  3. Well done job by the blogger, this is really informative, i have also shared to others, your analysis is very good and you have written everything in detail...
    Online Shopping In Pakistan