Rules change which email ReplyPen writes for, not who sends. Whatever a Rule does, the result is still a Draft that a person sends.
Why it matters
Most inboxes need no Rules at first: customer email that needs a reply gets a Draft, and email that needs none is skipped automatically. Rules are for the patterns you notice later, such as a supplier whose updates keep getting Drafts, or a large customer whose email you never want skipped.
A Rule matches what is in the email, not who someone is in your records. To target a group of customers, match their domains or addresses; to target a topic, match the words customers use for it.
An example
Two Rules a support inbox often starts with: Skip for the domain of a tool that sends status updates, and Always draft for any email whose body mentions “refund” or “cancel”, so those always get a Draft someone reads.
More in Rules.