Are there any postal service Rules rules that prohibit taping something to the outside of an envelope?

My dad just mailied out a 4 or 5 page letter in a clasp envelope , on the outside of the envelope he taped a sticker that was about the size of a small bumper sticker

by taped I mean he laid the sticker down then put some clear tape over it .



will the postal service accept letters like that?



do thaey return to sender or just toss it outAre there any postal service Rules rules that prohibit taping something to the outside of an envelope?
As long as proper postage is included, I don't think there is any reason the Post Office would not send this envelope. However, the envelope will be going through some automated machinery for processing as well as being handle by many people along its journey so there is a good chance the tape will not hold up and the sticker will fall off on its own.Are there any postal service Rules rules that prohibit taping something to the outside of an envelope?
Yes, I do it all the time. As long as it isn't bulky and will go through the machines, it should be fine. Even then, they will still try to salvage it and get it to you.Are there any postal service Rules rules that prohibit taping something to the outside of an envelope?
As long as the stamp is visible, they will accept almost anything.