Exchange 2010 SAN Certificates
Wildcard Certificate is for sub domain
SAN certificate is for multi domains.
The certificate error that pops up shows you that it is finding the certificate on your company’s public website.
The Autodiscover service is a mechanism that can do several things.
Automatic Mailbox Creation
Redirects Outlook 2007/2010/2013 clients to point to the correct server in which their mailbox is located
Provides URLs to Web Services for Outlook 2007/2010/2013
There are one of two fixes for this:
Add the domain.com to your Public Facing Website’s certificate. That way, Outlook makes a successful connection to https://domain.com, determines it’s not Exchange, and will fallback to attempting autodiscover via https://autodiscover.domain.com. (Preferred Option for obvious secure reason)
Disable SSL on the public facing website’s root. That way, no cert error would ever happen and Outlook will happily fallback to using autodiscover.domain.com. (Less Preferred Option for obvious secure reasons. Be absolutely sure you do not require any kind of encrypted security on your website if you go this route).