A. Check the Overview tab to determine whether the prospect is unmailable.

B. Check the Lists tab to determine whether the prospect is on the recipient list or any suppression lists.

C. Check the Audits tab to see if the prospect was on the correct lists when the email was sent.

D. Check the Profile tab to make sure the prospect has the right engagement program profile.

E. Check the Lifecycle tab to confirm whether the prospect entered the engagement program before the email was sent.