As it stands at the moment, using an automatic record creation rule to create cases from an incoming mail queue will not prefil both the Customer and Contact field on a created record if the sending email address is both a pre-existing Contact in the system and placed into one of the emailaddress(1/2/3) fields on the account form. As confirmed by a Microsoft support case, the Account will take precedent, therefore only the Account will be place on the created record, instead of the Account and Contact.

In my mind, this is not expected system behaviour, but currently that is how Dynamics will work, confirmed by the PG. I would like this changed so that it will create a record using both the Account and Contact record linked correctly instead of just the Account.