I've got my esg sitting in front of gsuite and I'm constantly getting emails showing up as rejected with the following delivery detail
host ASPMX.L.GOOGLE.COM[xxx.xxx.xxx.xxx] said: 550-5.7.1 [xxx.xxx.xxx.xxx 12] Our system has detected that this message is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to Gmail, 550-5.7.1 this message has been blocked. Please visit 550-5.7.1 https://support.google.com/mail/?p=UnsolicitedMessageError5505.7.1 for more information. q195si64619itb.58 - gsmtp (in reply to end of DATA command)
If you need more details about our setup please inquire. I'll be happy to pass them along, I didn't wanna throw out a data dump right up front.