Custom voicemail subject based on voicemail group

Is it possible to change the subject, or at least add a custom variable to the subject, when a voicemail goes to more than one person?

;Urgent voicemail group

I’d like to have something where the email would do one of the following:
Display the mailboxes the voicemail went to.
Have it show ‘URGENT’ in the subject if it was sent to that group.
Show the email addresses of all the people the voicemail went to.

What happens is that we don’t know if a voicemail was urgent or not or who got it, so we forward them to each other and it ends up making a mess.

I’m using postfix as the mailer. Is this possible to do or do I need to do some script for postfix?