Unless you are a dealer, you can't legally mail a handgun.
From the BATF website FAQ:
http://www.atf.treas.gov/firearms/faq/faq2.htm#b1
B. UNLICENSED PERSONS
(B1) To whom may an unlicensed person transfer firearms
under the GCA? [Back]
A person may sell a firearm to an unlicensed resident of his
or her state, if the buyer is not prohibited by law from
receiving or possessing a firearm, or to a licensee in any
state. A firearm other than a curio or relic may not be
transferred interstate to a licensed collector. [18 U. S. C
922( a)( 3) and (5), 922( b)( 3), 27 CFR 178.29]
(B2) From whom may an unlicensed person acquire a firearm
under the GCA? [Back]
A person may only buy a firearm within the person's own
state, except that he or she may buy a rifle or shotgun, in
person, at a licensee's premises in any state, provided the
sale complies with state laws applicable in the state of
sale and the state where the purchaser resides. [18 U. S. C
922( a)( 3) and (5), 922( b)( 3), 27 CFR 178.29]
(B3) May an unlicensed person obtain a firearm from an
out-of-state source if the person arranges to obtain the
firearm through a licensed dealer in the
purchaser's own state? [Back]
A person not licensed under the GCA and not prohibited from
acquiring firearms may purchase a firearm from an
out-of-state source and obtain the firearm if an arrangement
is made with a licensed dealer in the purchaser's state of
residence for the purchaser to obtain the firearm from the
dealer. [18 U. S. C 922( a)( 3) and (5), 922( b)( 3), 27 CFR
178.29]
(B8) May a nonlicensee ship a firearm through the U. S.
Postal Service? [Back]
A nonlicensee may mail a shotgun or rifle to a resident of
his or her own state or to a licensee in any state. Handguns
are not mailable. A common or contract carrier must be used
to ship a handgun. A nonlicensee may not transfer any
firearm to a nonlicensed resident of another state. The
Postal Service recommends that longguns be sent by
registered mail and that no marking of any kind which would
indicate the nature of the contents be placed on the outside
of any parcel containing firearms.
(B9) May a nonlicensee ship a firearm by carrier? [Back]
A nonlicensee may ship a firearm by carrier to a resident of
his or her own state or to a licensee in any state. A common
or contract carrier must be used to ship a handgun. In addition, Federal law requires that the carrier be notified that the shipment contains a firearm and prohibits common or contract carriers from requiring or causing any label to be placed on any package indicating that it contains a firearm. [18 U. S.C. 922( a)( 2)( A) and 922( e), 27 CFR 178.31]
(B10) May a nonlicensee ship firearms interstate for his or
her use in hunting or other lawful activity? [Back]
Yes. A person may ship a firearm to himself or herself in
care of another person in the state where he or she intends
to hunt or engage in any other lawful activity. The package
should be addressed to the owner. Persons other than the
owner should not open the package and take possession of the
firearm.