Originally Posted by
chollie
2 data points.
IIRC, SEA has at least one mailbox landside, right across from a checkpoint.
I was told (when I went looking for one and asked) that there are landside mail boxes at ATL. There supposedly used to be a mailbox airside in the international terminal but it was moved for security reasons.
Conclusion: One cannot rely on having a mailbox convenient to security lines.