As you choose or create a recipient segment for your email send-out, you don’t need to use the ‘Reachable by email’ or ‘Accepts email’ criteria.
Engage will automatically only include recipients that both accept email and have a valid email address registered on their contact card.
"Reachable by email"
If a contact is “Reachable by email”, it means that they accept email, the email field on their contact card is not empty, and the email is not blocked.
If a contact “Accepts email”, they have given their consent to receiving emails. However, they don’t necessarily have a valid email address registered. In that case, they will not be counted as “Reachable by email”.