It's a security thing. So, instead of jumping on that email bandwagon all for nothing, why not try one of the links mentioned in that bulletin, which I will include here:
Instead of sending an “Any Wounded Soldier” letter or package to Walter Reed, please consider making a donation to one of the more than 300 nonprofit organizations dedicated to helping our troops and their families listed on the "America Supports You".
Other organizations that offer means of showing your support for our troops or assist wounded servicemembers and their families include:
To Our Soldiers
For individuals without computer access, your local military installation, the local National Guard or military reserve unit in your area may offer the best alternative to show your support to our returning troops and their families. Walter Reed Army Medical Center will continue to receive process and deliver all mail that is addressed to a specific individual.
Finally, Michelle recommended Operation Undergarment. They collect underwear, pajamas, and monetary donations to help wounded soldiers. At their website, they have the bios of the soldiers they are helping.
And just remember, when you lend a hand, say a prayer too! It costs absolutely nothing, and is worth a whole lot.