What is reverse DNS (rDNS) and FCrDNS, and how do they impact email sending?
Summary
What email marketers say11Marketer opinions
Email marketer from EasyDMARC shares that FCrDNS (Forward-confirmed reverse DNS) means that your hostname has both an A record that resolves to your IP address and a PTR record that resolves back to your hostname. It's an important trust signal for email servers.
Email marketer from MXToolbox responds that when an email is sent, the recipient server performs an rDNS lookup on the sending server's IP address. If the rDNS record is present and matches the sending domain, it increases the likelihood that the email will be accepted.
Marketer from Email Geeks explains that when the MTA connects to Google, it will say ehlo mta1.yourdomain.com, and Google will check the IP, retrieve the PTR record, and expect it to match.
Email marketer from Email Marketing Forum explains that mail servers that have a reverse dns entry that points to a domain name that does not match the sending domains will typically be marked as spam by mail providers.
Email marketer from StackExchange highlights that email servers using dynamic IPs often have generic or non-existent rDNS records, which can cause email delivery issues. It's generally recommended to use a static IP with a proper rDNS setup for reliable email sending.
Email marketer from SparkPost Blog shares that rDNS helps improve email deliverability by confirming that the sending server is authorized to send emails on behalf of the domain in the 'From' address. A mismatch or absence of rDNS can flag emails as suspicious.
Email marketer from WebHostingTalk Forums responds that if you are unable to setup a reverse dns record due to restrictions from your web hosting company, you should send mail via a SMTP relay as you cannot guarantee deliverability without one.
Marketer from Email Geeks shares that a PTR record is the reverse of an A record. If mta1.yourdomain.com points at 10.1.1.2, there would be a PTR record for 10.1.1.2 that points to mta1.yourdomain.com.
Email marketer from Mailjet Blog responds that rDNS is crucial for email authentication. When an email server receives a message, it performs an rDNS lookup to verify if the IP address matches the domain sending the email. This helps to prevent spoofing and phishing attacks.
Marketer from Email Geeks explains that your provider (email, CRM) should take care of the FCrDNS requirement, as the requirement is that sending MTAs (email servers) have FCrDNS.
Email marketer from Reddit shares that having a proper rDNS setup significantly improves your email sending reputation. Many receiving mail servers will reject or flag emails from servers without a valid rDNS record.
What the experts say5Expert opinions
Expert from Word to the Wise explains that FCrDNS (full-circle reverse DNS) is the combination of forward DNS (a domain name resolves to an IP address) and reverse DNS (an IP address resolves back to the same domain name). It verifies that the server sending email is authorized to do so, improving deliverability.
Expert from Email Geeks says that if you want to keep using the machine/IP address then you probably want to get it a nailed down IP address and hostname, and set up reverse DNS for it.
Expert from Email Geeks notes that the rDNS issue Dave is experiencing with Gmail is due to sending mail from a machine not intended to be a mail server. Generic reverse DNS indicates consumer IP pools or misconfigured generic servers.
Expert from Spamresource.com says that a mail server that does not have a RDNS record or the record contains a generic hostname is a good indication the server is dynamic or a zombie and as such email from those servers will likely be flagged as spam.
Expert from Email Geeks clarifies that Google doesn't care if the reverse DNS is in your domain, it just wants it to not be loudly saying “I’m not a real mailserver, I’m a generic, unconfigured machine”.
What the documentation says4Technical articles
Documentation from AWS describes that to set up rDNS for Amazon SES, you must request Amazon to configure the PTR record for your dedicated IP addresses. This process verifies your control over the sending domain and improves deliverability.
Documentation from Microsoft Learn explains that Reverse DNS (rDNS) performs the opposite function of forward DNS. It resolves an IP address to a domain/hostname. It's used to verify the server associated with an IP address is authorized to send emails from the domain.
Documentation from RFC 1912 details that rDNS configuration involves creating PTR (pointer) records in the reverse DNS zone. These records map IP addresses to domain names and are essential for proper email server identification.
Documentation from DigitalOcean Community explains that rDNS records, specifically PTR records, reside in the in-addr.arpa domain and are managed by the owner of the IP address block. Setting up rDNS requires access to the IP's DNS settings.