Use cases
A first pass on a paste. You still decide what to mail.
Syntax mistakes
Lines missing an @ or a dot are flagged. They are not contacted.
Role and disposable
Locals such as info or admin, and a short disposable-domain list, are marked so you can drop them before you copy the rest.
What the score is
The share of lines that passed. It is not a mailbox ping and not a delivery promise.