The term 'MAIL OUT AGAIN' can be broken down into two crossword solutions: RESEND (6 letters) and RESENT (6 letters). RESEND is a verb meaning to send something again, usually after it has been returned or not received. RESENT is also a verb meaning to feel or express displeasure or indignation at something. Both words are related to the idea of sending something out again, either physically or emotionally.