Mailbox automatically Pinning every new incoming email - Desktop and Mobile

hi ev2522​ Since you've already tried recreating the Outlook profile, reinstalling Office, testing both Classic and New Outlook, and even testing different mobile clients, it sounds like the issue may be following the mailbox rather than being specific to a particular device or Outlook installation.

One thing I'd check is Outlook on the web. If the messages are also pinned there, that would point more toward a mailbox or service-side issue.

I'd also confirm that the messages are actually being pinned and not simply being sorted, flagged, or categorized in a way that makes them appear at the top.

If the behavior is consistent across Outlook desktop, web, and mobile, and you've already ruled out rules and policies, it may be worth opening a Microsoft 365 support case. There could be something being applied at the mailbox or service level that isn't exposed through the normal Outlook settings.

Given everything you've already tried, I wouldn't spend more time rebuilding Outlook profiles. The key is to determine whether the behavior follows the mailbox itself.