envelope stuffer

noun3

1. •
   One whose job is to manually insert sheets of printed paper into envelopes for mailing, especially as an example of a person whose work is menial and unfulfilling.

   • [C]arpel tunnel syndrome […] is seen in many workers who do repetitive tasks by hand, including telephone operators, envelope stuffers, cashiers and meat processors. — 1992
2. •
   A machine that mechanically inserts sheets of printed paper into envelopes.
3. •
   An advertisement, flyer, or other unsolicited printed material contained in an envelope received by mail.

   • Such an enclosure is sometimes thoughtlessly called an "envelope stuffer." — 1923