That’s a beauty of the open protocol, same as SMTP, no real solution but for relays to be smart about what and how they accept it. 

 So, there is or there isn’t a solution? 

 At protocol level, I don’t think so. At implementation level, many. 

 Like what 

 Like a good ‘ol’ spam filter and timing+content matching. 

 cEnSoRsHiP!!!! 🤣 

 You are smart for cat, now you are catching on 🤣😂