Spam Issues: ISPs want to halt spammers, so this is a huge destructive within their eyes. ISPs have a very very low tolerance for spam issues. You'll want to set up a threshold for spam complaints of under 0.1% and strictly adhere to it. The list of URIs for receivers https://mailwizz19900.ltfblog.com/26537967/email-deliverability-can-be-fun-for-anyone