Go to IIS7 and click on portal.domain.com - then go to Sites / Default Web site
Then on right hand side go to bindings and on "https-443-*" Edit and select the correct certificate
you will have to run these commands on the CAS Servers to change the
outlook provider to the new certificate name (E.g. the new cert i have
used below is for portal.entagroup.com)
Set-OutlookProvider EXPR -CertPrincipalName:"msstd:portal.domain.com"
Set-OutlookProvider EXCH -CertPrincipalName:"msstd:portal.domain.com"
setting relates to the account info in outlook - under account and more
settings / Connections Tab / Outlook anywhere / Exchange Proxy Settings
/ Proxy Server principal name