"Anything that evaporates cleanly will work fine."
Naptha/Zippo fluid is also a good carrier.
"But mostly I shoot some dry graphite lube into the lock from every opening, gently shaking for about 30 seconds to distribute it throughout the lock, and then bang the lock on a chunk of wood a couple times in case of clumps or whatnot."
Not an option for the lock on my mailbox.
Low grade naptha can leave an unpleasant oily residue on stuff. While not bad by itself, said residue seems to attract grit and dirt. Lighter fluid works well, however.
Re your mailbox locks, generally, I unmount the lock before doing maintenance. Only exception is padlocks.
Our Scout trailer and truck are parked outside, so the padlocks are out in the elements. Do you all still recommend a dry lubricant of these locks? I was thinking that something with water displacement properties would be a plus. In the past, a shot or two of WD-40 seemed to work for me...
WD-40 works fine, assuming you're fine with replacing the locks every 5-10 years depending. It will leave oily residue that attracts foreign matter.
You want to use PTFE if you're using an expensive lock or want all weather protection. Graphite will be fine for outdoors, just remember that a little goes a long way. Too much is bad. Compressed air is also your friend for blowing out foreign matter before lube. Dry silicone lubricant works, but I rarely use it. Graphite for most locks, Teflon/PTFE for the top shelf.