There are four main designations of emails addresses:
- Valid: meaning the email was tested and is an active address
- Catch-all: meaning the email server on the domain is set to "catch-all" so the only way to actually test the email is to send to it (only send to these emails when you trust the data provider)
- Invalid: email address does not work
- Trap: these are set-up by providers to catch people buying lists. Hitting one of this will knock out your sending