Hi guys, I've been struggling with this problem for 3 days now, I need help. I have rDNS and PTR setup on my VPS host solus working properly, I have my SPF TXT records in the DNS, I run checks on ANY and EVERY single DNS / rDNS website out there, I have GREEN lights down the board. Yet GMAIL is EXTREMELY STUBBORN. ----- Transcript of session follows ----- ... while talking to gmail-smtp-in.l.google.com.: >>> DATA <<< 550-5.7.1 [MYIP6IPADDRESSDISPLAYED HERE] Our system has detected that this message does <<< 550-5.7.1 not meet IPv6 sending guidelines regarding PTR records and <<< 550-5.7.1 authentication. Please review <<< 550-5.7.1 Bulk Senders Guidelines - Gmail Help for more information <<< 550 5.7.1 . d197si2224691oib.74 - gsmtp 554 5.0.0 Service unavailable How do I fix this regarding IP6 and PTR ??