Outlook’s Autodiscover Redirect Limit – Hybrid Autodiscover Breaking for Exchange Online Mailboxes / Remote On-Premises Mailboxes

Scenario:  After introducing additional Exchange On-Premises servers, we noticed that Autodiscover stopped working for our Exchange Online Hybrid mailboxes that were on computers internal to the domain. Using the ‘Test E-mail AutoConfiguration’ feature in Outlook, it would fail after the SCP/DNS autodiscover lookup.

Reason:  Outlook has an Autodiscover Redirect limit of 8-10 responses.  Being we had more than 10 servers in our Exchange Infrastructure, once it hit the response limit from each SCP lookup for each server, it would then fail all redirects thereafter. You do not need 100 SCP Failures if its going to fail after the first 10 servers.

Solution:  You can reduce the number of SCP lookup’s by performing any of the following.

1. Set the AutoDiscoverSiteScope value on each Exchange server so it only serves requests for each  AD Site via the following command:  Set-ClientAccessServer ExSrv1 -autodiscoversitescope NewYork   (Or a combination NewYork,Baltimore,Tampa)
2. Set the AutoDiscoverSiteScope to $null so it does not participate in SCP lookups via the following command: Set-ClientAccessServer ExSrv1 -AutodiscoverSiteScope $null
3. Set the AutoDiscoverServiceInternalURI to $null so it does not participate in SCP lookups via the following command: Set-ClientAccessServer ExSrv1 -AutodiscoverServiceInternalURI $null