You can mail a handgun through the mail. Conditions:
1. Do not use USPS, not worth the trouble, use FedEx, I’ve done it many times, must be actual FedEx facility and not a “store” where FedEx picks up; check their website or call local FedEx on phone for more info.
2. Must get buyer to get his FFL to mail you a copy of the FFL license, that is the only address you can legally mail it to. Check license is current.
3. Get paid buy USPS money order, best way to cover you both in case of lost/claims. Decide who pays shipping and insurance. Figure shipping cost before you finish the deal so no surprises.
4. Mail after you cash money order.
I’ve sold lots on Gunbroker this way. Armslist is great, too... no shipping. Get the procedures right for you state. First time is the hardest. Meet in a busy place.