Does anyone know if there is a mailbox at Barajas airport? Any place to drop something in the mail at the last minute? If so, do you remember where it's at? What terminal?

Hola SalaChic,
According to the official website of the airport, there is an actual post office on the main floor of T4 at Barajas. You can see a map here (and click on "Otros servicios" if it doesn't automatically come up).

I looked briefly at the T1 map, and it seems that there are mailboxes there on the first two floors. I didn't see anything for T3, but there is a also a mailbox in T2. Hope this helps!

Excellent. Thanks! I somehow couldn't find this page. My daughter and a friend will be traveling back to the states before us. Was thinking of giving her the sim chip out of one or our phones, putting it in a spare phone - and then they could use it so i know they make it to the airport ok, and/or they could call if they needed me. Then when they get to the airport, they put the chip in a padded envelope (pre-addressed and stamped....) and just drop it in a buzon. Anyone ever done this?

Oh, and double thanks because I would always get T1 and T2 mixed up. We fly USAir, which is always luggage check in counter #250. According to this lovely map, thats T1.So now I know. :-)

There's usually a mailbox at the booth where you submit your VAT refund paperwork, so the people can mail the forms back to the stores easily.