The Migration Impact of Office 365’s Max Message Size Increase from 25MB to 150MB

A lot of customers that I speak with on a daily basis are looking to migrate to Office 365 from a third-party hosting provider. In these types of environments, the hosting provider typically does not provide the rights required to migrate to Office 365 with the New-MoveRequest PowerShell cmdlet. This means that EWS or MAPI are often used as the transport mechanism to copy user mailbox data from the source hosted environment to Office 365.

The problem with this ‘copy’ based migration method is that the largest email message that could be moved into Exchange Online was 25MB. If you tried to move items larger than 25MB into Office 365 those messages would be rejected. As you can imagine – it is not hard to find users that have attachments in their mailbox that are larger than 25MB! Think about all those large PowerPoint slide decks, spreadsheets and videos that you have in “your” mailbox today!

Microsoft Office 365 Max Message Size Increase

But there is good news…

On April 15th, Microsoft announced a change to increase the allowed max message size to 150MB. This means that Office 365 administrators (with global admin privileges) can customize the current maximum message sizes that can be sent from and into Exchange Online from 25MB all the way up to 150MB!

This change can be completed on an organization-wide or even on a per-user basis. Specifically, Office 365 administrators can change the ReceiveMaxSize and SendMaxSize parameters on mailbox objects. This means that larger messages can be sent and received using the MAPI protocol (Outlook).

This is great news for Binary Tree customers that are looking to use E2E Expressto help copy mailbox data from a hosted environment into Office 365.

The video below will walk you through setting the required changes within Office 365 to set custom message sizes and utilizing E2E Express to copy large messages from your source environment over to Office 365.