From an AA postcard. I don't see any "offer only for the recipient of this mailing" language.
Code QPM10
Link to aa.com.
But it does say in the T&C:
*This offer is valid only for the
recipients of the AAdvantage August targeted insert. AAdvantage members must register for the promotion using promotion code QPM10 and become a new Admirals Club member between August 1, 2010 and September 30, 2010 to qualify for the 3,000 AAdvantage miles. Customer must be 18 years old to purchase an Admirals Club membership. This promotion is not valid for renewal of or adding a spouse to an existing Admirals Club membership. This AAdvantage mile offer cannot be used in conjunction with another discount or promotional offer. No retroactive credits apply. Admirals Club memberships are nonrefundable and nontransferable. AAdvantage miles will post within 6 – 8 weeks after then end of this promotional offer. These miles do not count toward elite status qualification.