I have Exchange 2010 and Office 365 set up in full hybrid mode. I have migrated some mailboxes over and mail flows as expected. Some of the mailboxes had a non default Receiving Message Size set while they were still on premises. Now that the mailboxes have been migrated this old limit is overriding any limit set in Exchange Online.
When looking at the Remote User Mailbox in the Exchange 2010 interface I can see the Maximum Message Size under the Mail flow Settings tab but it is greyed out and hidden behind a padlock indicating I don't have the permissions to modify it.
How do I go about changing these limits so that the migrated mailboxes respect the Exchange Online size limits?