Another word for reply mail

Here are some alternative words for "reply mail":

1. Response
2. Answer
3. Reply letter
4. Response letter
5. Acknowledgment
6. Rejoinder
7. Retort
8. Countermail
9. Feedback
10. Correspondence

Note that some of these words may have slightly different connotations or nuances, but they all generally refer to a written response or reaction to a previous message or communication.