Action: Identify large mail items - Messages larger than the allowed limit in Office 365 will not be migrated nor delivered, ...

Action: Identify large mail items - Messages larger than the allowed limit in Office 365 will not be migrated nor delivered, and the sender will receive a non-delivery report (NDR). Although message size limits can't be configured up, down, or on a per-user basis, administrators can create transport rules to limit the maximum size of any individual attachment. Learn more.