Should sending domains resolve to the same IP addresses as mail servers?
Michael Ko
Co-founder & CEO, Suped
Published 28 Apr 2025
Updated 17 Aug 2025
10 min read
The relationship between sending domains and the IP addresses of mail servers can often be a source of confusion, especially when dealing with email deliverability issues. It is a common question whether the domain you use to send emails should resolve to the same IP address that your mail server uses to dispatch those emails.
The short answer is, not necessarily. The core function of a sending domain is to establish identity and authenticity for your emails, while the mail server's IP address is where the email originates from. These two elements interact through various DNS records, but their direct resolution to the exact same IP address is not a strict requirement for good deliverability.
Understanding how DNS (Domain Name System) records work in conjunction with your mail servers is crucial. Many people assume a direct one-to-one mapping, but the reality is more nuanced, involving multiple layers of checks and validations that recipient mail servers perform.
Understanding DNS for email
When an email is sent, several DNS records come into play to verify the sender's legitimacy. The primary records involved are A records, MX records, and PTR records. Each serves a distinct purpose in directing and validating email traffic.
An A record, or Address record, maps a domain name to an IPv4 address. While a website's domain typically needs an A record to resolve to its web server's IP, a sending domain for email doesn't strictly need its A record to point to the IP address from which mail is sent. If it is purely a sending subdomain and not a website, it might not have an A record at all, which is often acceptable. For more details on this, you can look into whether an A record is needed for email sending domains.
MX (Mail Exchange) records specify which mail servers are responsible for accepting email on behalf of a domain. These records point to a hostname, which then resolves to an IP address via an A record. The important thing here is that the MX record points to the mail server that receives email for that domain, not necessarily the one sending it.
PTR (Pointer) records, also known as reverse DNS records, perform the opposite function of an A record, mapping an IP address back to a domain name. This is crucial for email deliverability. Mail servers often use PTR records to verify that the IP address sending the email is legitimate and not a spam source. The PTR record for your sending IP should resolve to the canonical hostname of your mail server, not necessarily your sending domain. This process is commonly referred to as reverse DNS resolution.
Record type
Purpose
Example
A record
Maps a domain or subdomain to an IPv4 address. Essential for web servers, optional for purely sending subdomains.
mail.example.com IN A 192.0.2.1
MX record
Specifies mail servers responsible for receiving email for a domain.
example.com IN MX 10 mail.example.com
PTR record
Maps an IP address back to a hostname. Crucial for anti-spam checks and verifying sending server identity.
1.2.3.4.in-addr.arpa IN PTR mail.example.com
The relationship between sending IPs and domains
The confusion often arises because the From: address (the domain visible to the recipient) does not need to have an A record that resolves to the IP address of the sending mail server. For example, if you send an email from no-reply@yourdomain.com, the domain yourdomain.com or no-reply.yourdomain.com does not need its A record to point to the sending IP. In fact, if it's a subdomain purely for sending, it might not have a public A record at all.
What truly matters for deliverability is that the IP address sending the email has a valid PTR record (reverse DNS) that points back to a legitimate hostname associated with the sending server. This hostname typically belongs to your email service provider (ESP) or your own mail server, such as mta.esp.com. This specific hostname is then expected to have a forward A record that resolves back to the same sending IP, establishing a critical two-way link known as forward-confirmed reverse DNS (FCrDNS).
Understanding rDNS impact
A missing or misconfigured PTR record is a major red flag for recipient mail servers. Many, including those run by Google and other large providers, may reject or spam emails originating from an IP without proper rDNS. It's a fundamental anti-spam measure to prevent spoofing and identify legitimate senders.
IP reputation and authentication
While the sender domain (the domain in the From: header) does not need to resolve to the sending IP, the sending IP needs to have a good reputation. This is why proper authentication (SPF, DKIM, and DMARC) is so important, as it ties your sending IP to your domain's reputation.
The importance of email authentication
Email authentication protocols like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) are designed to verify sender identity. SPF checks if the sending IP is authorized to send mail on behalf of the domain listed in the Return-Path (also known as the MailFrom or bounce address). DKIM uses a digital signature to ensure the email content hasn't been tampered with and verifies the signing domain. DMARC ties these together, instructing recipient servers how to handle emails that fail SPF or DKIM checks. You can learn more in our simple guide to DMARC, SPF, and DKIM.
These authentication methods primarily rely on DNS records for the domain in the Return-Path (for SPF) and the DKIM d= tag (for DKIM). The From: domain is what users see, but the underlying authentication mechanisms check other domains. This separation is why the From: domain does not need to resolve to the sending IP for proper authentication.
Asking clients to whitelist IP addresses is generally discouraged due to the dynamic nature of IP addresses used by many ESPs. If IPs change, clients have to update their allow-lists, leading to delivery interruptions. Instead, advise clients to whitelist based on domain authentication, which is more stable and robust. This approach aligns with industry best practices advocated by major mailbox providers, including Microsoft and Google.
IP whitelisting
Process: Clients add your sending IP addresses to their email security filters' allow-list.
Maintenance: Requires frequent updates if your ESP changes IP addresses, which is a common occurrence.
Effectiveness: Less reliable as a long-term strategy for deliverability.
Domain authentication (SPF, DKIM, DMARC)
Process: Clients configure their systems to trust emails authenticated by your domain using DNS records.
Maintenance: Minimal, as DNS records (SPF, DKIM, DMARC) for your domain are stable, even if IPs change.
Effectiveness: Highly effective and the industry standard for verifying email authenticity.
Handling client inquiries about IP resolution
It is perfectly normal for multiple domains to be associated with a single IP address, especially in shared hosting environments or when using an ESP. An email service provider (ESP) will typically use a pool of IP addresses for various clients. Your email's From: domain might not directly map to an IP, but the IP that sends the email will be part of the ESP's infrastructure and will have its own PTR record. You can use the same sending domain on multiple email platforms or IPs, provided your DNS records are correctly configured for authentication.
When a client observes that your sending domain does not resolve to the IP address you provided, or that it resolves to a different IP, it is often due to this separation of concerns. The A record for your From: domain might point to a web server, or not exist at all if it's purely a sending subdomain without web content. The IP addresses you provide for whitelisting are the actual sending IPs, not necessarily the IPs your From: domain resolves to.
The key is to ensure that the Return-Path domain (which SPF checks) correctly authorizes the sending IP. This domain is often a subdomain managed by your ESP, such as bounces.yourdomain.com. Your SPF record for this domain lists the authorized IPs or include mechanisms of your ESP. For example, if you use SendGrid, your SPF record will likely include include:sendgrid.net.
The client's query likely stems from a misunderstanding of how SPF works. SPF validates the Return-Path domain, not the From: domain. For robust email deliverability, focus on ensuring proper SPF, DKIM, and DMARC alignment, and confirm your PTR records are correctly configured for the actual sending IPs.
Example SPF record for SendGriddns
v=spf1 include:sendgrid.net ~all
Maintaining deliverability and reputation
Ensuring your sending domains and mail servers are properly configured is a continuous effort. While the exact IP match between a sending domain's A record and the mail server's outbound IP is not strictly necessary, the overall DNS configuration needs to be coherent and verifiable. Any discrepancy can potentially lead to emails being flagged as spam or even added to a blocklist (or blacklist).
Monitoring your domain and IP reputation is key. Tools exist to check if your domains are associated with any email blacklists or blocklists, which would significantly impact your deliverability. Regularly reviewing your DNS settings and authentication reports (DMARC reports, for example) can help identify issues before they become major problems.
Views from the trenches
Best practices
Always ensure your sending IP has a correctly configured PTR record that resolves to a valid hostname.
Prioritize SPF, DKIM, and DMARC for email authentication, as these are critical for sender verification.
Educate clients about domain-based whitelisting over IP-based whitelisting for stability and effectiveness.
Common pitfalls
Expecting your 'From' domain's A record to directly match your sending IP address, which is not required.
Relying solely on IP whitelisting for email delivery, leading to issues with IP changes or shared IP environments.
Neglecting to update SPF records when changing ESPs or adding new sending sources, causing authentication failures.
Expert tips
Regularly monitor your DMARC reports to identify authentication issues and potential domain misuse.
Verify your SPF and DKIM configurations frequently, especially after making any DNS changes or migrating ESPs.
Understand that the email 'From' domain and the envelope 'Return-Path' domain serve different purposes in email flow.
Expert view
Expert from Email Geeks says sending domains should always resolve to an IP address unless there's an intentional break in the configuration.
2023-11-21 - Email Geeks
Expert view
Expert from Email Geeks says the IP addresses that sending domains resolve to are unrelated to the IP addresses from which email is actually sent, so these resolved IPs don't need to be in SPF records.
2023-11-21 - Email Geeks
Key takeaways for reliable email delivery
The short answer to whether sending domains should resolve to the same IP addresses as mail servers is no, not directly. While the mail server's IP needs a proper PTR record that resolves to its hostname, and that hostname needs a matching A record, the domain in your From: header does not need to resolve to the same IP as the mail server. This is a common point of confusion, but it doesn't impact deliverability as long as your email authentication is correctly set up.
Focus on robust SPF, DKIM, and DMARC implementation, ensuring that the Return-Path domain aligns with your SPF records, and the DKIM d= domain is correct. This is the foundation of trustworthy email sending and will prevent most deliverability issues that arise from DNS queries.
Ultimately, if you're experiencing email deliverability problems, look beyond simple IP resolution for your sending domain. Instead, perform a thorough check of your entire email authentication setup and your sending IP's reputation, as these are the true indicators of your email's legitimacy.
Google and other large providers, may reject or spam emails originating from an IP without proper rDNS. It's a fundamental anti-spam measure to prevent spoofing and identify legitimate senders.
Microsoft and Google.
