From their services page:
A U.S. mailbox is found in Terminal A on the Departures Level, pre-security. It is just inside the entrance.
As of August 2018 they have updated their terminal maps!
- Terminal A: Pre-security Level 2 Departures, by door A-201 (just inside the exterior door to the drop-off lanes)
- Nothing marked for Terminals B, C, D or E.
This is most likely a standard USPS drop box.
IAH is huge, and most flyers will not frequent Terminal A in the normal course of travel to/from/through IAH. Getting to this dropbox will most likely require a round trip on a people mover that can take up to fifteen minutes in one direction (assuming from Terminal D/E; Terminal B and C may be closer). Re-clearing security may take an extended period of time and may require you to transit to another terminal. Allow an hour from Terminal D/E if you want to drop a letter off.
Consider dropping off mail prior to visiting the airport, or waiting to reach another airport if you are transiting IAH.
Last Updated 19 August 2018