Summary
Experts and documentation across the email industry agree that sending domains do not need to resolve to the same IP addresses as mail servers. The consensus emphasizes the paramount importance of domain authentication using SPF, DKIM, and DMARC protocols for ensuring deliverability. Reverse DNS (PTR records) for sending IPs are also vital. The advice to whitelist IPs directly without domain authentication is considered outdated and potentially confusing.
Key findings
- Authentication is Key: SPF, DKIM, and DMARC are the primary mechanisms for authenticating email and ensuring deliverability; their correct implementation is more crucial than IP resolution.
- IP Resolution is Secondary: The IP address that a sending domain resolves to is not directly relevant to email deliverability, as long as authentication protocols are in place.
- Importance of PTR Records: Reverse DNS (PTR records) for sending IPs should map back to the sending domain to establish trust.
- Whitelisting Best Practices: Recipients should whitelist authenticated mail from the sending domain rather than relying solely on IP addresses.
Key considerations
- Implement SPF, DKIM, and DMARC: Properly configure SPF, DKIM, and DMARC for your sending domain to ensure authentication.
- Set up Reverse DNS: Ensure your sending IPs have corresponding PTR records that point back to your domain.
- Avoid IP-Based Whitelisting: Discourage reliance on IP whitelisting without domain authentication, as IPs can change.
- Ensure Domain Validity: Verify that your sending domain is valid and properly configured for email sending.
What email marketers say
10 marketer opinions
Multiple email marketing experts and documentation sources agree that sending domains do not need to resolve to the same IP addresses as mail servers. Instead, the focus should be on proper domain authentication using SPF, DKIM, and DMARC, as these are the primary mechanisms for verifying sender identity and ensuring email deliverability. Reverse DNS (PTR records) for mail server IPs is also important.
Key opinions
- IP Irrelevance: The IP address to which a sending domain resolves is not directly related to email deliverability.
- Authentication Focus: SPF, DKIM, and DMARC are critical for authenticating the sender and ensuring emails are not flagged as spam.
- Reverse DNS Importance: Reverse DNS (PTR records) for mail server IPs is more important than the A record of the sending domain.
- Reputation Building: Sending domains are primarily used for authentication and reputation building, not direct IP-based delivery.
Key considerations
- SPF Record Accuracy: Ensure your SPF record accurately lists all authorized sending sources (mail servers and ESPs).
- DKIM Setup: Implement DKIM to digitally sign your emails, further verifying their authenticity.
- DMARC Policy: Configure DMARC to instruct receiving mail servers on how to handle emails that fail SPF and DKIM checks.
- PTR Record Configuration: Verify that your mail server IPs have properly configured reverse DNS (PTR records) pointing to your sending domain.
- Monitor Reputation: Actively monitor your domain and IP reputation to identify and address any deliverability issues.
Marketer view
Email marketer from EmailOctopus Blog shares that the sending domain is primarily used for authentication (SPF, DKIM) and reputation building. It doesn't necessarily need to resolve to the same IP as the mail server; proper authentication is more crucial.
19 Apr 2023 - EmailOctopus Blog
Marketer view
Email marketer from StackOverflow answers question clarifying that the 'sending domain' is primarily for identifying your brand, whereas SPF/DKIM records associated with your actual mail servers handle authentication. The two aren't directly linked IP-wise.
21 Feb 2025 - StackOverflow
What the experts say
5 expert opinions
Email deliverability experts generally agree that sending domains do not need to resolve to the same IP addresses as the mail servers sending the email. They emphasize that focusing on proper authentication mechanisms like SPF and DKIM is more crucial. One expert highlights the importance of reverse DNS (PTR records) for sending IPs. IP whitelisting is discouraged in favor of domain authentication.
Key opinions
- IP Resolution Not Required: Sending domains are not required to resolve to the same IP addresses as mail servers.
- SPF/DKIM Priority: SPF and DKIM are the primary mechanisms for authenticating email and ensuring deliverability.
- Reverse DNS Importance: Reverse DNS (PTR records) for sending IPs is crucial for establishing trust and deliverability.
- Domain Authentication over IP Whitelisting: Domain authentication using SPF and DKIM is preferred over IP whitelisting for long-term maintainability.
Key considerations
- Implement SPF and DKIM: Ensure SPF and DKIM are correctly configured for your sending domain.
- Configure Reverse DNS: Set up reverse DNS (PTR records) for your sending IPs to point back to your domain.
- Prioritize Domain Authentication: Encourage recipients to whitelist authenticated mail from your domain rather than specific IP addresses.
- Avoid Misleading Advice: Be cautious of advice suggesting IP whitelisting without proper domain authentication.
Expert view
Expert from Spam Resource explains that the goal is to authenticate email communications by using SPF to publish a list of authorized IP addresses for a domain. It also says if you add multiple domains in your from header, you must make sure you include all of the parent domains in the SPF record to authenticate the email.
7 Apr 2024 - Spam Resource
Expert view
Expert from Email Geeks explains that relying on IP whitelisting leads to updating issues when IPs change. He highlights that SPF and DKIM exist to avoid IP-based sender authentication.
20 Aug 2024 - Email Geeks
What the documentation says
5 technical articles
Email deliverability documentation consistently states that sending domains are primarily used for sender identification and authentication purposes. Resolving to the mail server's IP address is not a requirement. SPF, DKIM, and DMARC are the key technologies for verifying sender identity and domain alignment, rendering the IP address of the sending domain less critical for email deliverability.
Key findings
- Authentication over IP: Email authentication (SPF, DKIM, DMARC) is more important than the IP address of the sending domain.
- Sender Identification: Sending domains are primarily used for identifying the sender in the 'MAIL FROM' field.
- Domain Alignment: DMARC focuses on domain alignment between the 'From:' header and SPF/DKIM, not IP address alignment.
- SPF Validation: SPF validates the sending server, not the sending domain's host IP.
Key considerations
- Implement SPF: Ensure SPF is configured correctly to authorize sending sources for your domain.
- Implement DKIM: Deploy DKIM to sign your emails cryptographically.
- Implement DMARC: Set up a DMARC policy to instruct receiving servers on how to handle unauthenticated emails.
- Ensure Domain Validity: Ensure the sending domain is valid and properly configured for authentication purposes.
Technical article
Documentation from DKIMProxy.org details that DKIM relies on cryptographic signatures verified against a public key published in DNS for the sending domain. It is designed to address sender authentication without requiring direct IP address correlation.
6 Nov 2022 - DKIMProxy.org
Technical article
Documentation from Microsoft Learn explains that SPF records authenticate sending sources for a domain. The focus is on authorized mail servers, not necessarily requiring the sending domain's A record to match those servers' IPs. SPF validates the sending server, not the sending domain's host IP.
22 Apr 2024 - Microsoft Learn
Do PTR records and HELOs impact email deliverability?
How do I configure reverse DNS (rDNS) with multiple IP addresses for email sending?
How do I perform a reverse DNS lookup and interpret the results?
Why am I getting Google bounces due to PTR record issues, even though my setup seems compliant?
Why does Google Postmaster Tools reputation change lag behind sending behavior?
