New SSL certificate needed for SBS2011 with 5 email domains

Hello Experts - we have an SBS2011 server with a self-signed certificate which has been working fine until we created autodiscover DNS records to fix calendars for Outlook Anywhere staff.

We have a single static public IP address

Out set up is like this:

the cn of the existing cert is remote.company.com.au

Outlook Anywhere proxy server :  remote.company.com.au

This server also collects mail for 5 other domains.

The autodiscover DNS address for each of these domains looks like:


Autodiscover.company.com.au
Autodiscover.company2.com.au
Autodiscover.company3.com.au
Autodiscover.company4.com.au
Autodiscover.company5.com.au
Autodiscover.company5.com.au

We have one static IP address

Outlook now produces this error about 30 seconds after opening (see attached)



I checked ClientAccessServer and WebServicesVirtualDirectory settings in Exchange and they look fine

I think we need a new certificate but don't know enough about them

Someone has suggested a UN / SAN certificate such as from:

http://www.geotrust.com/ssl/ssl-certificates-san-uc/ 

Any help appreciated

thanks
Outlook-Cert-Error.png