A Mail Strike works in basically the same way as the Air Strike; the direction of the bombing (from the left or from the right) can also be changed, like the Air Strike. However, the Mail Strike does not drop small, normal bombs, instead dropping five letter bombs which do damage of about 50 HP per letter. These letter bombs are affected by wind, and flutter from left to right slightly at random, meaning that a mail strike is a very imprecise weapon; it is best used for bombing a very wide area.
Using The Mail Strike
The same as the Air Strike, just select the area where you want to drop it, but be careful of the wind as it can be affected by wind.
In Worms 3D
In Worms 3D, the weapon appears as the "Lottery Strike". It cannot be unlocked for use in normal game modes except the Full Wormage, but it can be used through the tutorial "The Driving Range".