During migration to Office 365, you have noticed the following error:
“Failed to write Mail:[Title of your message] ErrorMessageSizeExceeded”
The mail is larger than the Exchange Web Services permissions in the Office 365 target.
Change the maximum size of the message allowed in your target mailbox. You can use the following PowerShell scripts:
Step 1. Determine the current user’s settings:
Get-Mailbox email@example.com | fl mailboxplan,maxsendsize,maxreceivesize
Step 2. Set up new limitations for the whole Office 365 tenant:
Get-MailboxPlan | Set-MailboxPlan -MaxSendSize 150MB -MaxReceiveSize 150MB
These limitations will be applied only to newly created users. If you have already created your users, use the script from Step 3.
Step 3. Increase limitations for an existing user:
Get-Mailbox | Set-Mailbox -MaxReceiveSize 150MB -MaxSendSize 150MB
To check if modifications are done correctly, run again a command from the Step 1 and restart your migration if needed.
Once the migration is done, you can always set up the limitations to the original values if needed.