Ok,

I finally bit the bullet and purchased a SAN Certificate for Exchange 2007 so that I dont get any more problems with security errors etc. There was a small problem though, The SAN consisted of

CN = domain.com
SAN (Subject Alternative Name) = autodiscover.domain.com & rpc.domain.com & webmail.domain.com

Due to the way outlooks connects over RPC/HTTPS you need to make sure you update the MSSTD Record to reflect the CN on the certificate

  • Set-OutlookProvider EXPR -Server $null -CertPrincipalName msstd:domain.com