I always drop it in the designated drop box on camera in front of the public library.
Postal Service employees never use those blue boxes for their own letters, by the way. Too many postal carriers have been mugged and had the keys stolen for them to keep up with changing the locks. People just go in and steal everything, soak the ink off checks and rewrite them ... when they're not being purely vandalous and pouring liquids inside the boxes, or setting them on fire.