I keep getting a MAILER-DAEMON error.

From: Lenny Thomas  8/19/17

 to Gregg, ACGNJ 
Verizon, aol, and many of the Microsoft servers will return an error message to many of the free mass email protocols, such as the mass emailers from many website mailing programs. The messages will range from. "Scanners find content to contain spam", to " email account unavailable" . Even after you go through the trouble to fill out their trouble forms the problem will return and persist. 
They seem to blacklist most of these protocols under the guise of offering better spam control. Many of the commercial mass mailing programs like Mail Chimp are not so blocked. One of the solutions for this problem seems to be to have your email server use a port other than 25 to send email. Gmail and Yahoo didn't seem to be using this for spam protection scheme yet.


    

Links:

SPOT_UsersGuide_2007_10_16.pdf

last updated 16 Aug  2017