The changes are synchronized to the mailbox on the Exchange server as soon as the system connects to the internet.
Thus, when you draft a message, make changes to Outlook in Mac while offline, these modifications are saved in the local OLM file.
It allows users on Mac to keep working in Outlook even if the system is on airplane mode or not connected to the internet. Outlook on Mac stores a synchronized copy of mailbox on the Exchange server in an OLM or Outlook for Mac file.
