Search a list of mailboxes

I hope this is a simple request.
I don't know how to invoke a list (csv file) to search mailboxes.

For example I can dump a Distribution List members into a csv.
But then i'd like to search those members mailboxes for a specific message.

Search-Mailbox "user 1" -SearchQuery 'Subject:"spam email"' -estimateresultonly

Instead of searching for this one user mailbox, i'd like to use a csv and in that csv are all the DL members.