This Customer Support Ruling discusses envelopes included in copies of a Periodicals publication.
Domestic Mail Manual (DMM) 207.3.3 details the types of permissible mailpiece components that may be included with copies of a publication mailed at the Periodicals rates.
Empty, all-purpose envelopes (which are usually designed for reply purposes) and sealed or unsealed envelopes that contain printed advertising sheets may be bound into copies of Periodicals or affixed to the pages. Envelopes need not be bound into or affixed to the pages if individual copies of the publication are enclosed in a mailing wrapper and may be inserted loose in copies of unbound publications.
Envelopes may not be used to convey products or product samples through the mails at Periodicals prices as prohibited in DMM 184.108.40.206. If such nonpermissible enclosures are placed inside of envelopes, they are subject to the applicable Standard Mail prices under DMM 703.9 or as a Ride-Along under DMM 207.15.
Envelopes included in Periodicals publications are eligible for Periodicals prices as weight when they are subscription related and as advertising if they contain other advertising matter.
Headquarters, US Postal Service
Washington, DC 20260-5015