there's the "franking" privilege for some of the politicians....

From Wikipedia...

""Privilege" franking is a personally pen-signed or printed facsimile signature of a person[11] with a "franking privilege" such as certain government officials (especially legislators) and others designated by law or Postal Regulations. This allows the letter or other parcel to be sent without the application of a postage stamp. In the United States this is called the "Congressional frank" which can only be used for "Official Business" mail."