What is the purpose of a return address on an envelope?

The return address on an envelope serves the crucial function of allowing undeliverable mail to be returned to the sender. If for any reason the recipient cannot be reached, whether due to an incorrect address or any other delivery issue, postal services utilize the return address to send the mail back to the original sender. This is particularly important for ensuring that important documents and communications are not lost and can be redirected appropriately.

The other options do not align with the primary purpose of a return address. For instance, indicating a sender's favorite color or providing marketing information does not relate to the functionality of an envelope. Similarly, while postage may need to be affixed for mailing, it is unrelated to the return address's role in the mail delivery process.