How do I configure reverse DNS (rDNS) with multiple IP addresses for email sending?
Summary
What email marketers say9Marketer opinions
Email marketer from ServerFault responds by advising to avoid having multiple IPs pointing to a single hostname, because email servers validate rDNS to protect from spam.
Email marketer from DNS Records shares that to setup rDNS, create an A record that links your domain name to your IP address. Then, use your DNS management to create a PTR record pointing your IP address to the domain name.
Email marketer from Email on Acid explains that rDNS is like a caller ID for email. It confirms that a message came from the server it claims to originate from which prevents email spoofing. To implement, set up your DNS records to point your IP to your domain name.
Email marketer from SparkPost explains that reverse DNS is important for email deliverability as it helps verify that the sending IP address is associated with a legitimate domain, increasing sender reputation.
Email marketer from StackOverflow responds by clarifying that for each IP address, a corresponding PTR record must point back to a valid hostname. Using the same hostname for multiple IPs is not recommended for email sending.
Email marketer from MXToolbox shares that each IP address used for sending email should have a corresponding PTR record that resolves to a hostname within your sending domain. This helps establish trust with receiving mail servers.
Email marketer from Reddit explains that you need to create a separate A record and PTR record for each IP address. Each IP should have a unique hostname associated with it.
Email marketer from Email Geeks shares that you are totally free to choose a prefix and recommends a pattern such as mailX or mtaX, transactionX for simplicity.
Email marketer from Postmark explains that rDNS increases your email deliverability rates. When receiving servers see that your sending IP has rDNS configured and points back to your domain, it builds trust between sending servers and receiving servers.
What the experts say6Expert opinions
Expert from Email Geeks suggests setting up hostnames for each IP and using that hostname when publishing the rDNS.
Expert from Email Geeks shares that when they were at Salesforce, they would have used `mta.ml.hostname.com` and `mta2.ml.hostname.com` and suggests Mailgun will have to advise, but expects a similar setup would be appropriate.
Expert from Spam Resource explains that if you are using a shared IP, you will likely not be able to control reverse DNS (rDNS). You need to use a dedicated IP for rDNS configuration.
Expert from Word to the Wise explains that Reverse DNS records are vital to ensuring good delivery as mail providers and anti-spam systems will check to see if the RDNS of the IP matches up to the hostname sending the mail. They also share that RDNS (PTR) records should point to the same server or domain that the sending server is using.
Expert from Email Geeks suggests including a SPF TXT record for those hostnames. Recommends the SPF can be very simple: “v=spf1 ip4:111.222.111.222 -all”.
Expert from Email Geeks shares to check headers to verify what the machine is actually using in the EHLO value.
What the documentation says5Technical articles
Documentation from Linode explains that reverse DNS maps an IP address back to a domain name. For multiple IPs, each IP needs its own PTR record pointing to a unique hostname.
Documentation from RFC 1035 explains that PTR records are used in the domain name system to map an IP address to a name. This is especially relevant for email servers verifying sender identity through reverse DNS lookups.
Documentation from Cloudflare explains that PTR records are used to resolve IP addresses to domain names. Reverse DNS lookups use PTR records to verify the source of a connection which helps in anti-spam measures.
Documentation from Vultr shares that for each IP address you want to set rDNS for, you need to create a corresponding PTR record. Each PTR record links an IP address to a hostname.
Documentation from DigitalOcean explains that to configure reverse DNS, you must create A records that point your desired hostname to your IP addresses, then use your DNS provider's interface to set up the PTR records pointing your IPs to the hostnames.