Variable envelope return path

Let's pretend you're sending a letter to your friend. You put the letter in an envelope and write your friend's address on the front. Then you take the envelope to the post office and give it to the nice person behind the counter. They put a stamp on it and send it on its way.

Now, when your friend gets the letter, they might want to send something back to you. They put their letter in an envelope, write your address on the front, and take it to the post office. But here's the thing - their envelope doesn't have a stamp on it yet. It needs to be sent back to you somehow, but it's not its own letter like yours was.

That's where the variable envelope return path comes in. It's like a special way for the post office to know that your friend's envelope is supposed to be sent back to you. It's called "variable" because the post office doesn't always know what address it needs to go to - it depends on who sent the original letter.

So when your friend takes their envelope to the post office, they tell the person behind the counter that it's a "variable envelope return path" envelope. The post office person can then put their own special stamp on it that says "return to sender" and has your address on it. This way, when the envelope gets to you, you know exactly who it's from and can write back to them.