do some people have a letter in their address #?

Yes, this is a perfectly valid address in the US system. This indicates that the person lives in an area that has not yet been platted to the reference point of the local municipality; rather, it's taken from the county / parish / borough mapping.

This often happens in rural areas where there are established roads to support home delivery (mailboxes), but for whatever reason, the local post office hasn't seen a need to extend either street addressing or route / box numbers there. I once had an address like this when we were incorporated into a new city being built, but the city had not yet finalized plans for the street map within the city limits.

The "5" is a sort of area designator; "N" is for "north"; "267" is the current "house number". This is roughly equivalent to "267 N. Fifth St.", except that "Fifth" may be a swath including several established roads.

An address is anything the resident says it is. I know a fellow who lives in the forest and couldn't get reliable mail delivery until he added "Timberlost" to his address. Apartments often have odd combinations of letters and numbers that make perfect sense when you see the layout of the buildings. If someone says his address is 5N267 I would assume that means building N wing 5 and the street number is 267.

http://pe.usps.com/businessmail101/addressing/chec...

Write on the envelope, now no longer ordinary at this cope with, go back to sender. If its a company you ought to deliver back about 5 letters and then they take be conscious that the guy now no longer lives at that cope with.

It could be.