For the USPS, "bulk mail" is a term of art, more properly bulk presorted mail.

There are several categories: 500 pieces of first-class mail, 200 pieces or 50 lb as "USPS Marketing Mail", Parcel Select Ground (50-piece minimum per mailing), presorted and carrier route sourted bound matter (300 pieces), library mail (300 pieces), media mail (300 pieces).

<https://www.usps.com/business/business-shipping.htm>

The tradition of discounting certain mailings, especially publications (e.g., newspapers) and books dates to the very beginning of the US postal service and was established by Benjamin Franklin.

<https://www.history.com/news/us-post-office-benjamin-frankli...>

I strongly suspect crote wrote "email" intending "mail". Particularly as little email carries stamps or requires sorting by a post office.

I've nearly done the same several times in this thread myself. "Mail" really doesn't roll off my fingertips so readily these days.

One example might be an energy company (they tend to be big) that will send bills to a significant percentage of any residential area in its catchment area, probably four times a year at around the same time for everyone. Now repeat for water companies, phone companies, local government et cetera.