We have 2 FE servers which are servicing all our other backend mailbox servers fine except a new one we recently deployed. We stood up a Native AG and a single backend MB server. When we hit the FE server and put in the credentials, we're getting:
The System Cannot Find the File Specified (I turned off friendly HTTP error messages in IE)
This Native site is part of our Org but the users are members of a child domain with a different SMTP address, however, other users in the domain with a different SMTP address can authenticate.