January 16th 2015: Added an update below this article...
Earlier this week, Microsoft announced a change in the maximum supported item size to migrate to Exchange Online.
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 service.
The previous limit was 25 MB. Customers needed to check if items larger than 25 MB existed in the mailboxes before that could be migrated to Exchange Online. The users then needs to be informed to export the item from his mailbox and store it on a file share. Alternatively administrators can perform the export from the Exchange side.
Microsoft already updated the Exchange Online Limits document to include the new 'Message size limit - migration' value.
There has been some confusion on the subject of migration. Some people, including me, assumed that this new limit was applied to mailboxes being moved with the Mailbox Replication Service. This would limit this improvement to Hybrid Migrations. How about Outlook Anywhere based Cutover and Staged migrations, and how about the IMAP migration? Or 3rd party migration tools using EWS to migrate the data over to the Exchange Online mailboxes?
Exchange MVP Henrik Walter is very clear:
Does the new 150 MB message size limit apply to third party tools?
That depends but typically no. The reason for this is because most third party tools provisions the mailbox (meaning it wll have the limit for the mailbox plan enforced) prior to migration unlike MRS based moves.
MCM/MCSM Gare Steere believes the change applies to both MRS based moves and IMAP migrations. That leaved Staged and Cutover migration with the current 25 MB limit.
My expectation is that the changed limit will apply to MRS move for sure, that makes perfect sense because this is the most 'enterprise' friendly way to migrate mailboxes. I would expect Microsoft to keep trying to deliver the best experience for this migration method. The other native migration tools are being used for small scale migrations and have already severe limitations, I think Microsoft will give less priority to improve this methods.
At this time it's not possible to share a definitive answer because there's no official statement other than the initial announcement. Why don't we just test then? Because changed like are being rolled out in Office 365 over a certain period of time, it's not immediately available for all tenants. So if we test and find the test to fail, it can be because the change has not been applied to our tenant yet.
In the mean time I will post when I have more information. If you did more information, please let me know in the comments section!
My sources tell me (how cool does that sound!) there is much confusion and discussion with Microsoft internally. The internal communication gives the impression this only applies to MRS moves however it remains unclear how this will work exactly. If the limit is applied on the store level, can a user move the large items between folders?
And then there's this issue with hybrid moves some people reported in December:
The value of property 'MaxReceiveSize' exceeds the maximum allowed for user *****. The allowed maximum receive size is 150 MB.
+ CategoryInfo : InvalidArgument: (firstname.lastname@example.org :MailboxOrMailUserIdParameter) [New-MoveRequest], RuleValidationException
+ FullyQualifiedErrorId : [Server=BLUPR02MB147,RequestId=99b351c5-8fae-4372-a3c4-8575ab1e16d2,TimeStamp=12/18/20149:19:03 PM] [FailureCategory=Cmdlet-RuleValidationException] 6264EEEB,Microsoft.Exchange.Management.RecipientTasks.NewMoveRequest
Microsoft confirmed this issue and had fixed it in less then a week, however I am sure that this error has something to do with the changed message size limit. Is this a confirmation that the new limit is enforced by the mailbox move process on the MRS? Interesting...