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
9 marketer 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.
3 Apr 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.
2 Sep 2023 - DNS Records
What the experts say
6 expert 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.
29 Mar 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.
9 Sep 2022 - Email Geeks
What the documentation says
5 technical 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.
4 Feb 2022 - 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.
25 Feb 2022 - RFC Editor
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