1. qmail retry time
qmail-send delivery retry tims (remote)
2. Result
Retry after 400 seconds
retry after previous delay time + 800 seconds, …
1-hour : 3 times
4-hour : 6 times
12-hour : 10 times
24-hour : 14 times
3. Proof
cat /var/log/maillog
Q. How to identify if it is the same mail?
A. MID