Next qmail 16

Delivery Schedule

Typically, the first delivery is tried right away (t=0)
If it encounters a temporary failure, qmail-send tries again in 100 seconds (t=100)
If it fails again, the next try is at t=400
Then:

        Try #           Time (sec)  Elapsed since last try
        0                  0    
        1                100        1:40
        2                400        5:00
        3                900        8:20
        4               1600       11:40
        5               2500       15:00
        ...             ...        ...

The theory is that waiting around for an hour is not a big deal if the message is already old
For remote deliveries, multiply these times by 4
Eventually, qmail-send gives up
- It injects a bounce message into the queue
- It deletes the original message