We bought several certificates with 5 SAN on each for our several accepted domains on Exchange 2010. Now we realize that you can only have one certificate at a time for exchange services, which means we wasted our money :). Is there a way to use those certificates, i.e. to tell exchange for that domain use that certificate, or we have to buy one certificate with 15-20 SANs and throw away those that we bought earlier?
If you are using Outlook Anywhere, you'll need a single UC cert with an alternative name for autodiscover.domain.com and the public client access URL for each email domain.
If you're not using Outlook Anywhere (and are not using TLS transport) you only need to secure your OWA hostname.