Though you could accomplish this with message filters, my vote would be for using ldap group query with the incoming mail policy. You can have the Media-policy that checks if the recipients are a member of the Media group. If recipients aren't members of the group, they will use the Default policy. This is called message splintering by the way.
Then, once things have splintered into their appropriate incoming mail policies, you can have incoming content filters that drop the media attachments for the default policy while the Media policy allows them through.
Have you tried to create a policy allowing these file types and checking the recipients using LDAP group query ?
Then, insert a policy below this (the mentioned above) not allowing these file type for non-group members.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...