ENVS

Letter carriers (abbr.)

• GPO purchases

• Items that get stuffed and stamped: Abbr.

• Ltr. carriers

• Ltr. holders

• Mailers: Abbr.

• Places where SWAK may be written

• Pt. of SASEs

• Stationery store stock (Abbr.)

• They may be self-sealing: Abbr.

• They're often sent by the USPS

• Where to find the theme entries of this puzzle, briefly