The occasional Mac Mac user will sometimes see strange sync behavior with deleted items. The symptoms follow this pattern: you delete a message in Mac Mail and it vanishes as it should. However, you then look at another mail client such as on a mobile device or directly on the M365 portal at https://portal.office.com and that deleted message is still there? What gives?
It turns out, Mac Mail is trying to be convenient by giving you another option to recover (accidentally) deleted messages. In fact, it is only pretending to actually delete those messages simply by hiding them from your mailbox view.
There is a setting in Mac Mail that controls this behavior and is found in the “Preferences” menu under the Mail toolbar menu (top left) when you have Mac Mail open. Shown below is a screenshot of the Preferences->Accounts tab->Mailbox Behaviors tab. You will see the last checkbox item for “Store deleted messages on the server”. This has various timeframes/actions available in the drop down list, or you can simply uncheck that option.
Once updated appropriately (and understanding what is actually happening) things make a little more sense. Enjoy!
