I'm gonna be training nearly everyone in my department how to do the mail

I run the mail room in our workplace's procurement team and in a few months from now, I'm gonna be out of work for a good while, so my boss would like me to get the shipping/receiving guys up to snuff on how to do mail. Sure, I'll still have my two co-assistants around, but in the event that they're gone as well, he wants more hands with the right know-how around who can do it. Fair enough. It's not rocket science, so hopefully it doesn't have to take long with training each of them. Luckily, one of them used to be one of my assistants before she took an open shipping/receiving position. That's one less to train already, lol.