Hi Krwelliver,
The Autodiscover service uses a user's e-mail address to configure her or his profile automatically. Depending on the type of authentication configured on the server, Outlook for Mac users typically have to know only their e-mail address and account credentials during Exchange account configuration. When users provide their credentials to configure their Exchange accounts, Outlook for Mac connects to the Autodiscover service and the user account is automatically configured to use the Exchange mailbox.
In Outlook for Mac, the Autodiscover service keeps user account settings up-to-date after the account setup. When a user's Exchange Server information changes, Outlook for Mac reconfigures the user's profile automatically. Outlook for Mac checks for updates to the account settings:
1. Every time Outlook for Mac is started.
2. At a server-defined interval (by default, every hour) to make sure that the Exchange Server settings are always kept up-to-date.
3. When a user's mailbox is moved to another server. Autodiscover service will detect the move and update the settings.
4. During a network failure when Outlook for Mac tries to connect to the Exchange server.
Therefore it is a normal process that Outlook for Mac ensures the user account settings are latest by using Autodiscover service. Basically we click Allow, and if the Outlook for Mac works well you can ignore this message.
More information for your reference:
How the Autodiscover service works with Outlook for Mac 2011
Using Autodiscover with Exchange Online
Thanks,
Bourne Zhang