Outlook automapping is usually a good thing. Exchange marks a mailbox after a user receives full access permission for the mailbox. Autodiscover publishes details of the new access, and Outlook adds the mailbox to its resource list. But Some downsides exist, like the size of the OST, which mean that sometimes it’s better to add a mailbox manually to Outlook and forget about automapping.
https://office365itpros.com/2022/09/13/outlook-automapping/
