Mailbox, run before message is saved trigger

Hi,

I have a specific email from a customer that always should be merged with an existing request, this email have an PDF attachement. What would be the best way to merge this email?

"Mailbox, run before message is saved trigger" seems not to handle attachements, should I then use run after message is saved trigger and merge requests?

Would appriciate any suggestions how to do this.

Thanks!