I'm curious as to where enterprise vault gets it's server url for external access from.
It appears that the server name appears as <server name>.<doaim>.ad.local rather than <Server name>.<domain>.co.uk
This causes an issue for us when delploying the EV Outlook Web Application in Exchange 2013. This uses SSL and so the server name appears all wrong, in the cert we have the servername.<domain>.co.uk rather than <domain>.ad.local.
there's a config key for that called externalwebappURL in the web.config
you can also have a look here for more information. it's a centralized repository of all troubleshooting info for EV OWA. http://www.symantec.com/business/support/index?page=producttopic&landingTopicId=TOPIC45