I thought it was fine to mail guns, just handguns directly to an FFL.
If it's a rifle or shotgun, mail it to yourself..
Partially correct... If sending a firearm out of state, it
MUST go to an FFL or an authorized agent (usually LEO). Only FFL's or authorized agents can "mail" a handgun through the USPS. Long guns can be mailed by anyone.
When dealing with handguns, I'd do FFL-to-FFL for 2 reasons: 1) it gets documented, 2) the transfer fee with postage usually comes out cheaper than doing UPS or FedEx on your own.
For long guns, I just have the buyer send a copy of their ID with a signed bill of sale. Then send (USPS registered mail) it to an FFL of their choice.
**Mailing to yourself becomes illegal if someone else receives it at the destination. Meaning, you can not mail it to yourself c/o of someone else. You can send it to yourself, requiring your signature.
We can ship hand or long guns to a ffl ourselves if the receiving ffl is cool with it. In this case, the potential buyer's ffl only takes guns from ffls.
I'd make the buyer cover the fee on both ends or find an FFL that will accept.
ETA: Last time I checked (about a month ago), Carter said he'd do it for $20+postage.