Summary
Experts, marketers, and technical documentation collectively agree that matching reverse DNS (rDNS) with the SMTP banner and HELO/EHLO is crucial for optimal email deliverability. It serves as a fundamental check to verify the legitimacy of the sending server, build trust with receiving mail servers, and prevent emails from being flagged as spam. While one expert suggests that the rDNS to SMTP banner match mainly applies to inbound mail and may not always cause deliverability issues if mismatched, the broader consensus emphasizes that a correct configuration significantly enhances sender reputation and ensures mail stream accountability. Modern mail providers are becoming increasingly strict, making proper rDNS setup an essential best practice.
Key findings
- Verification of Sender: Matching rDNS and PTR records verify the legitimacy of the sending server's IP address and domain.
- Trust Building: A correctly configured rDNS record builds trust with receiving mail servers, improving deliverability rates.
- Spam Reduction: Proper rDNS setup reduces the likelihood of emails being marked as spam by recipient mail servers.
- Accountability and Traceability: Matching HELO/EHLO with rDNS allows mail admins to identify the source of the mail stream and increases trust.
- Industry Standard: Standards require valid domain names in HELO/EHLO commands, setting the stage for matching rDNS.
- Hubspot Specific Actions: If using Hubspot, you may need to ensure the PTR record points to a hostname that matches the SMTP banner by contacting support.
Key considerations
- Server Configuration: Ensure the mail server is correctly configured with matching hostnames in HELO, DNS, and PTR records.
- Cornerstone Practice: Treat correct rDNS configuration as a cornerstone of good email sending practices.
- Proactive Prevention: Use rDNS as a proactive measure to prevent your email from being flagged as spam, especially given increasingly strict mail provider policies.
- Return Address Mentality: Think of rDNS as a return address; emails without it are more likely to be treated as spam.
- Regular Monitoring: Regularly monitor and maintain your rDNS records to ensure ongoing accuracy and effectiveness.
What email marketers say
11 marketer opinions
The consensus from email marketers across various platforms is that matching reverse DNS (rDNS) with the SMTP banner is highly important for email deliverability. A properly configured rDNS record verifies that the sending IP address is authorized to send emails for the domain it claims to represent, building trust with receiving mail servers and reducing the likelihood of emails being marked as spam. While a mismatch may not always guarantee deliverability issues, it can raise red flags and negatively impact sender reputation. Aligning these elements is considered a basic and often trivial step towards ensuring optimal email delivery.
Key opinions
- Verification of Authorization: Matching rDNS verifies that the sending IP is authorized to send email for the domain.
- Building Trust: A matching rDNS record builds trust with receiving mail servers, improving deliverability.
- Spam Reduction: Properly configured rDNS reduces the likelihood of emails being marked as spam.
- Impact of Mismatch: A mismatch can raise red flags and negatively impact sender reputation, though it may not always result in rejection.
- Simple Implementation: Aligning rDNS with the SMTP banner is often a simple and cost-effective process.
- Basic step for deliverability: Ensuring the PTR record matches the SMTP banner is a basic step to improve deliverability
Key considerations
- HubSpot Configuration: If using HubSpot with a dedicated sending domain or IP, ensure the PTR record points to a hostname that matches the SMTP banner. Reach out to Hubspot support for more assistance on your dedicated sending domain.
- Stricter Mail Providers: As mail providers become stricter, ensuring the HELO/rDNS match is increasingly important.
- Return Address Analogy: Think of rDNS as a return address on a physical letter; without it, your email may be treated as spam.
- General Best Practice: Even if not strictly enforced, aligning HELO/EHLO and rDNS is a recommended best practice for email deliverability.
- For larger mail servers: A lot of larger mail servers will reject mail if reverse DNS is not properly configured
Marketer view
Email marketer from SparkPost explains that Reverse DNS (rDNS) is important because it helps to verify that the IP address sending the email is authorized to send email for the domain it claims to represent. A matching rDNS record builds trust with receiving mail servers and improves email deliverability.
5 Jul 2023 - SparkPost
Marketer view
Email marketer from Mailjet shares that a reverse DNS lookup is a query to determine the domain name associated with an IP address. It helps email servers verify the authenticity of incoming emails. If the reverse DNS record doesn't match the sending domain, it can negatively impact deliverability.
10 Feb 2024 - Mailjet
What the experts say
5 expert opinions
Experts emphasize that aligning reverse DNS (rDNS) with the SMTP banner and HELO/EHLO is important for email deliverability and sender reputation. While one expert notes it primarily applies to inbound mail and a mismatch might not break things, it's generally seen as a sign of a well-configured server. Correct rDNS helps verify the legitimacy of the sending IP address, build trust with receiving mail servers, and ensures mail administrators can identify and trust the source of the mail stream. SpamResource particularly highlights it as a cornerstone of good IP/domain reputation and an increasingly important anti-spam measure, as spammers rarely configure it correctly.
Key opinions
- Verification of Sender: Matching rDNS verifies the legitimacy of the sending IP address and domain.
- Trust Building: Proper rDNS configuration builds trust with receiving mail servers.
- Reputation Enhancement: Correct rDNS is a cornerstone of a good IP and domain reputation.
- Anti-Spam Measure: rDNS helps in filtering out spam as spammers rarely configure it properly.
- Identification of Source: Matching HELO/EHLO with rDNS allows mail admins to identify the responsible party for the mail stream.
- Inbound vs. Outbound Relevance: rDNS and SMTP banner matching are more relevant to inbound mail checking but still a good sign for outbound mail configuration.
Key considerations
- Server Configuration: Ensure your mail server is properly configured, including matching hostname in HELO and DNS.
- Competence and Professionalism: Aligning rDNS shows competence and professionalism to receiving mail servers.
- Cornerstone: Consider correct rDNS as fundamental to good email practices.
- Proactive Spam Prevention: Use rDNS as a proactive measure to prevent your mail from being flagged as spam.
- Administrator Confidence: Ensure your HELO/EHLO matches rDNS/PTR to provide confidence to mail administrators receiving your emails.
Expert view
Expert from Email Geeks explains that unless they are confused, reverse DNS matching SMTP banner only applies to inbound mail. While not a big deal, it's a sign the mail server may not know its hostname.
10 Oct 2021 - Email Geeks
Expert view
Expert from Email Geeks explains that for deliverability, sender server configuration and DNS are key. A matching hostname in HELO and DNS is a good sign. While a mismatch won't break anything, aligning them looks more competent and professional.
13 Nov 2022 - Email Geeks
What the documentation says
4 technical articles
Technical documentation from Google, Microsoft, the RFC Editor, and cPanel consistently emphasizes the importance of having a valid PTR record that matches the sending IP address to your domain for email deliverability. A mismatch can lead to emails being marked as spam. A matching PTR record verifies the legitimacy of outbound emails, builds trust, and improves deliverability rates by confirming the server is authorized to send emails on behalf of the domain. While the RFC doesn't explicitly focus on matching reverse DNS, it mandates that SMTP servers send a valid domain name in the EHLO or HELO command.
Key findings
- Crucial for Legitimacy: Matching PTR records are crucial for verifying the legitimacy of outbound emails.
- Impacts Deliverability: Matching PTR records improve deliverability rates and help avoid spam filters.
- Builds Trust: Matching PTR records build trust with receiving mail servers.
- Domain Authorization: Matching PTR records confirm that the server is authorized to send emails on behalf of the domain.
- Standards Requirement: RFC standards require SMTP servers to send a valid domain name in EHLO/HELO commands.
Key considerations
- PTR Record Setup: Set up a valid PTR record that matches the sending IP address to your domain.
- Domain Name in HELO/EHLO: Ensure that the domain name sent in the EHLO or HELO command is a valid address record or a valid literal address.
- Regular Checks: Regularly check and maintain your PTR records to ensure they remain accurate.
- Hostname Correspondence: Create PTR records that correspond to the mail server's hostname to further improve deliverability.
Technical article
Documentation from Microsoft Docs shares that having a matching PTR record for your mail server's IP address pointing to your domain is important for verifying the legitimacy of your outbound emails. It helps in building trust and improves deliverability rates, as it confirms that the server is authorized to send emails on behalf of the domain.
20 Aug 2023 - Microsoft Docs
Technical article
Documentation from Google Workspace Admin Help explains that setting up a valid PTR record that matches the sending IP address to your domain is crucial. A mismatch can cause email to be marked as spam.
31 Mar 2023 - Google Workspace Admin Help
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