Last week on April 15th, Microsoft announced a change to increase the allowed max message size to 150 MB. This means that Office 365 administrators (with global admin privileges) can customize the current maximum message sizes that can be sent and received from Exchange Online from 25 MB all the way up to 150 MB!
Office 365 administrators can change the SendMaxSize and ReceiveMaxSize parameters on mailbox objects. This means that larger messages can be sent and received using the MAPI protocol (Outlook).
The Problem Statement
Many people that I’ve talked to or articles that I have read are strictly focusing on the use cases for sending 150 MB messages. Yes, I agree that the old Exchange administrator in me winces when I think about end users sending 150 MB files through an Exchange system. But in reality, I do not think this was the sole driving force behind Microsoft making this change.
A lot of people are missing the beauty of this change! Here is what I mean.
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 25 MB. If you tried to move items larger than 25 MB 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 25 MB! Think about all those large PowerPoint slide decks, spreadsheets and videos that you have in “your” mailbox today!
This new change can be completed within your O365 tenant on an organization wide or even on a per user basis as you can see below:Change the mailbox plan:
Set-MailboxPlan ExchangeOnlineEnterprise-c7c130d6-15d9-4b85-9723-450db9d42aae -MaxSendSize 150MB -MaxReceiveSize 150MB
Get-Mailbox -Resultsize Unlimited | Set-Mailbox -MaxSendSize 150MB -MaxReceiveSize 150MB
Now you do have to keep in mind that these max send and receive limits are applied differently depending on the mail client that you choose to use. For instance, with Outlook you can send a single 100MB attachment if your O365 send limits are set properly.
I feel like this is a great change for those customers that have been looking to move to O365 but are currently utilizing a third-party hosting provider for their email. Before this change these customers would have to remove any attachments over 25MB or make specific plans for them before using EWS or MAPI to copy the mailbox data from the source environment to their new O365 tenant. I feel like this is a terrible change if customers simply want to send 150MB files. Shudder. That goes against everything us Exchange administrators have been preaching and educating the business about for years.