Who likes having to add tons of domains to their SAN certificate? The answer.. Nobody!! If you’ve got 100 domains in your Exchange org, hell – even 15 – and want to use AutoDiscover, then you’ve got a task on your hands.
Unless you take a look at my two part article series on MSExchange.org! This article shows off an easy technique (and multiple ways to achieve it) to use AutoDiscover Redirection to allow you to have a simple SAN certificate (e.g. one with just mail.domain.com and AutoDiscover.primarydomain.com) and have as many domains work properly with AutoDiscover as you like.