So I followed the tutorial below The Perfect Server - Ubuntu 16.04 (Xenial Xerus) with Apache, PHP, MySQL, PureFTPD, BIND, Postfix, Dovecot and ISPConfig 3.1 Now, I can send mail locally to myself but I am not able to send it elsewhere, it just says it sent. I've tried sending to an @hotmail.com and an @gmail.com. Also I am not able to send from those addresses to the domain from my website, nothing on my roundcube inbox. I've tried looking multiple places with no solution No response to the @hotmail.com and no email in that inbox either with the @gmail.com I get the following: Final-Recipient: rfc822; email address Original-Recipient: rfc822; email address Action: failed Status: 5.7.1 Remote-MTA: dns; gmail-smtp-in.l.google.com Diagnostic-Code: smtp; 550-5.7.1 [2601:1c1:8701:6042:3154:dcb3:849e:976f] Our system has detected that 550-5.7.1 this message does not meet IPv6 sending guidelines regarding PTR 550-5.7.1 records and authentication. Please review 550-5.7.1 (link removed due to post requirements) for more 550 5.7.1 information. pl3si14328917pac.22 - gsmtp"