What is the difference between first class mail and standard mail?

First class mail:

-Takes 1-3 days for the post office to deliver to mail box.

-First class mail is forward to recipient, if there has been a recent change of address.

-Return mail will be sent back to the return address on mail piece.

Standard mail:

-Takes 8 to 21 days for the post office to deliver to mail box.

-There is no return mail for standard mail.