MainSleaze

If you are somebody who habitually receives abuse complaints from random third parties, consider twice before outsourcing all your mail reception to third parties such as Google or Microsoft.

<person@ESP_domain>: host ESP_domain.relay1g.spamh.com[174.37.103.12]
said: 554 5.7.1 URL/Phone Number Filter - CUSTOMER'S_DOMAIN (in reply to
end of DATA command)

Even your own spam filter thinks your customer is a spammer. So you don’t get the complaints. Brilliant.