MailMate has a correspondence layout/pane that automatically shows all the emails received from the sender that sent the current selected email. We can then select one or more of these and delete in one swoop (or do any other action).
The Correspondence layout allows you to immediately see any messages in any correspondence similar to the currently selected message(s).
Are there any other email clients that have this feature?
Caveat: That applies only to Apple Mail, and (of course) Mailmate (but you need to set Mailmate store mail in an indexable location) Mail apps like Spark etc are not going to integrate with BusyContacts