What are the attachment size limits when migrating to Office 365 with ODME? (4345919)

What are the attachment size limits when migrating to Office 365 with ODME?

What are the attachment size limits when migrating to Office 365 with On Demand Migration for Email (ODME)?

ODME uses Exchange Web Services (EWS) to migrate data to Office 365. EWS is very similar in underlying functionality to Outlook Web Access (OWA). Microsoft provides guidance about attachment size limits in Office 365 in the following blog article:

Office 365 now supports larger email messages—up to 150 MB

The following snippet was copied from the bottom of  this blog article, under the heading "Technical Details" on August 16, 2016:

First, as a message routes from mail system to mail system it can get larger than when it started. This happens because as a message traverses different mail systems, transcoding (or Base64/MIME conversion) may occur, most commonly between on-premises Exchange and the cloud. This results in a 33 percent larger message than when it left your outbox. Even though the maximum allowed message size is now 150 MB, this is the maximum message size threshold after any potential transcoding has occurred. If your message is going to get transcoded, then it will be limited to 112 MB maximum. Yet, not all messages are subject to transcoding. For example, most messages sent between mailboxes hosted within Office 365 won’t get transcoded, so they can be a full 150 MB in size.

Second, email clients differ in their support for sending large messages. For example, in Outlook, assuming no transcoding is involved, you can attach a 150 MB size file and send it, and assuming the recipient is also hosted in the cloud and is configured to receive 150 MB size messages they’ll receive it. OWA, however, restricts the size of the message you can send to 25 percent less than the configured allowed maximum send size. It does this proactively to account for the possibility there might be a message size increase due to transcoding. For example, if your maximum allowed send size is set to 100 MB then using OWA you can only send up to 75 MB maximum. Additionally, in OWA, each attachment can be no larger than 25 MB. So with a 100 MB maximum send size, using OWA you could attach and send up to three 25 MB files in a single message. These conditions may change in the future, so be sure to check the official Office 365 documentation for the latest on the message size support provided by various email clients.

Previous version of ODME: By default, ODME is set strip any attachment larger than 10 MB in size and replace it with a text file place holder. A Service Request can be created to increase this limit to the 25 MB maximum allowed by Office 365. Increasing the limit beyond the 25 MB limit allowed by Office 365 will incur "Unable to process attachment" errors within the ODME migration log. In summary, when migrating to Office 365 with ODME each attachment can only be 35 MB in size by default. If Microsoft is able to increase the size limits in your Office 365 tenants web.config file, then please contact Quest Support with the new limits so that limits within ODME can be adjusted accordingly.