How do I configure reverse DNS (rDNS) with multiple IP addresses for email sending?

Summary

Configuring reverse DNS (rDNS) with multiple IP addresses involves creating distinct A and PTR records for each IP, ensuring each IP maps back to a unique hostname. This setup is crucial for email deliverability, as it verifies the sending server's legitimacy, builds trust with receiving mail servers, and prevents spoofing. Using dedicated IPs is essential, as shared IPs typically lack rDNS control. Including SPF TXT records for hostnames enhances security. Verify the EHLO value used by the sending machine. Avoid pointing multiple IPs to the same hostname.

Key findings

  • rDNS Improves Deliverability: Reverse DNS is critical for email deliverability as it verifies the association between the sending IP and the domain, building trust with receiving servers.
  • Unique Hostnames & Records: Each sending IP address requires unique A and PTR records, ensuring it maps back to a distinct hostname.
  • Dedicated IPs Required: Dedicated IPs are necessary for rDNS configuration since shared IPs usually don't allow control over reverse DNS.

Key considerations

  • DNS Record Configuration: Use your DNS provider's interface to configure A and PTR records, mapping hostnames to IPs and vice versa.
  • SPF Records for Security: Include SPF TXT records for each hostname to enhance security and explicitly authorize sending IPs.
  • EHLO Verification: Verify the EHLO value used by the sending machine in email headers to ensure it aligns with your DNS configuration.
  • Avoid Shared Hostnames: Avoid pointing multiple IP addresses to the same hostname, as this can negatively affect deliverability.

What email marketers say
9Marketer opinions

Configuring reverse DNS (rDNS) with multiple IP addresses is crucial for email deliverability. Each IP address must have a unique hostname, requiring separate A and PTR records. This setup helps verify the sending IP's association with a legitimate domain, building trust with receiving mail servers and preventing email spoofing. It's generally advised to avoid pointing multiple IPs to a single hostname.

Key opinions

  • Importance of rDNS: Reverse DNS is essential for verifying the legitimacy of the sending server and improving email deliverability by establishing trust with receiving mail servers.
  • Unique Hostnames Required: Each IP address used for sending email must have a unique hostname associated with it to ensure proper rDNS configuration.
  • A and PTR Records: Setting up rDNS involves creating both A records (linking domain to IP) and PTR records (linking IP to domain) for each IP address.

Key considerations

  • Avoid Shared Hostnames: Do not point multiple IP addresses to the same hostname, as this can negatively impact email deliverability due to failed rDNS validations.
  • Prefix Conventions: When creating hostnames for multiple IPs, consider using a consistent naming convention (e.g., mail1.yourdomain.com, mail2.yourdomain.com) for simplicity and organization.
  • Email Spoofing: Ensure that correctly configured rDNS can prevent email spoofing and make mail servers more trustworthy.
Marketer view

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.

November 2024 - ServerFault
Marketer view

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.

July 2023 - DNS Records
Marketer view

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.

May 2022 - Email on Acid
Marketer view

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.

May 2021 - SparkPost
Marketer view

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.

December 2021 - StackOverflow
Marketer view

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.

October 2023 - MXToolbox
Marketer view

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.

May 2023 - Reddit
Marketer view

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.

May 2024 - Email Geeks
Marketer view

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.

May 2024 - Postmark

What the experts say
6Expert opinions

Configuring reverse DNS (rDNS) with multiple IP addresses involves setting up individual hostnames for each IP, which aids in email delivery. Using dedicated IPs is crucial, as shared IPs typically don't allow rDNS control. It's important to ensure rDNS records align with the sending server's hostname, and including SPF TXT records for hostnames can enhance security. Verifying the EHLO value used by the sending machine in email headers is also recommended. A common approach involves creating hostnames such as `mta.yourdomain.com` and `mta2.yourdomain.com`.

Key opinions

  • Dedicated IP Requirement: You need a dedicated IP address for rDNS configuration; shared IPs usually don't allow control over rDNS.
  • Hostname Alignment: Reverse DNS records should align with the hostname used by the sending server to ensure proper validation by mail providers.
  • Individual Hostnames: Setting up unique hostnames for each IP address is essential for proper rDNS configuration when using multiple IP addresses.

Key considerations

  • SPF Records: Consider including SPF TXT records for each hostname to enhance security. `v=spf1 ip4:your.ip.address -all`.
  • EHLO Verification: Check email headers to verify the EHLO value used by the sending machine, ensuring it aligns with your DNS configuration.
  • Example Hostname Convention: Use hostnames like `mta.yourdomain.com` and `mta2.yourdomain.com` to differentiate between IP addresses.
Expert view

Expert from Email Geeks suggests setting up hostnames for each IP and using that hostname when publishing the rDNS.

October 2022 - Email Geeks
Expert view

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.

April 2024 - Email Geeks
Expert view

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.

August 2021 - Spam Resource
Expert view

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.

July 2022 - Word to the Wise
Expert view

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”.

November 2021 - Email Geeks
Expert view

Expert from Email Geeks shares to check headers to verify what the machine is actually using in the EHLO value.

February 2024 - Email Geeks

What the documentation says
5Technical articles

Configuring reverse DNS (rDNS) with multiple IP addresses requires creating A records to map hostnames to IP addresses and PTR records to map IP addresses back to those hostnames. Each IP needs its own PTR record pointing to a unique hostname. This setup verifies the sender's identity during email communication, which is a crucial step in anti-spam measures.

Key findings

  • A and PTR Records Essential: Configuring rDNS involves creating both A records (hostname to IP) and PTR records (IP to hostname).
  • Unique PTR per IP: Each IP address needs its own PTR record pointing to a unique hostname.
  • rDNS for Verification: Reverse DNS lookups, facilitated by PTR records, verify the source of a connection, aiding in anti-spam efforts.

Key considerations

  • DNS Provider Interface: Use your DNS provider's interface to configure the PTR records properly.
  • Accurate Mapping: Ensure accurate mapping between IP addresses and hostnames in both A and PTR records.
  • Anti-Spam Implications: Properly configured rDNS is crucial for email servers verifying sender identity, thereby improving email deliverability and reducing the likelihood of being flagged as spam.
Technical article

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.

January 2024 - Linode
Technical article

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.

September 2021 - RFC Editor
Technical article

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.

June 2024 - Cloudflare
Technical article

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.

April 2024 - Vultr
Technical article

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.

June 2024 - DigitalOcean