After we moved from our own server to Linode I started getting these bounce messages from Comcast. Reverse DNS just means that if you have an IP address you can find the domain associated with it. In my case I have lots of domains at the same IP address but use one for sending mail. I didn\u2019t know what a PTR record is so I looked it up. Wikipedia says that \u201cIPv4 uses the in-addr.arpa domain and the ip6.arpa domain is delegated for IPv6. The process of reverse resolving an IP address uses the pointer DNS record type (PTR record).\u201d<\/p>\n
On our old server we did our own DNS hosting and all of the info was contained in a file. So I knew about MX records, A records, etc. Linode uses a control panel to do the DNS setup so the setup is a bit different, but the same info is there. I had an A record for the domain that was sending the email, mail.machinename.com, and one for the domain that the email was coming from i.e. support@mycompany.com.<\/p>\n
I checked with intoDNS<\/a> to make sure that everything was set up correctly and I did in fact have a PTR record that pointed to the right place. \u201cYour reverse (PTR) record: 192.168.255.173.in-addr.arpa -> mycompany.com\u201d.<\/p>\n The clue came in a bounce from a different domain. The message said that the reverse DNS for 2500:34e80::f03c:92ee:fg70:ab93 was not found. It turns out that this is an IPv6 address. It appears that Linode is using an IPv6 address for the port I send mail from. To get a reverse DNS set up for that address I needed to set up an AAAA record in the Linode control panel, wait a while for it to propagate to Linode\u2019s DNS servers, then set up reverse DNS for the IPv6 address.<\/p>\n I waited a day for the change to propagate and now my Comcast emails are going through fine.<\/p>\n","protected":false},"excerpt":{"rendered":" After we moved from our own server to Linode I started getting these bounce messages from Comcast. Reverse DNS just means that if you have an IP address you can find the domain associated with it. In my case I have lots of domains at the same IP address but use one for sending mail. … Continue reading all mail servers must have a PTR record with a valid Reverse DNS entry<\/span><\/a><\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-1894","post","type-post","status-publish","format-standard","hentry","category-computers"],"_links":{"self":[{"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/posts\/1894","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1894"}],"version-history":[{"count":1,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/posts\/1894\/revisions"}],"predecessor-version":[{"id":2996,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/posts\/1894\/revisions\/2996"}],"wp:attachment":[{"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1894"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1894"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1894"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}