Will changing subdomain IP to main domain IP affect email deliverability?
Matthew Whittaker
Co-founder & CTO, Suped
Published 28 Jul 2025
Updated 17 Aug 2025
8 min read
The question of how changes to your domain infrastructure impact email deliverability is a common one. Specifically, many wonder if changing a subdomain's IP address to match the main domain's IP will affect their email sending reputation and inbox placement. It's a valid concern, as IP addresses are fundamental to how email servers identify and evaluate incoming messages.
While IP addresses are indeed part of your email infrastructure, their direct link to deliverability, especially for non-sending subdomain IPs, is often misunderstood. The short answer is that, in most cases, changing a subdomain's A record to match your main domain's A record will likely have minimal direct impact on your email deliverability, provided that the IP in question isn't your email sending IP. Modern email filtering systems place more emphasis on domain reputation than on the general IP addresses associated with web properties.
IP reputation versus domain reputation
Historically, IP reputation was the primary factor in determining whether an email landed in the inbox or the spam folder. Internet Service Providers (ISPs) heavily relied on the sending IP's history to gauge its trustworthiness. If an IP had a history of sending spam, it would quickly be blocklisted (or blacklisted), leading to deliverability issues for all senders using that IP.
However, the landscape has evolved significantly. Today, mailbox providers like Google and Yahoo (among others) place a much greater emphasis on domain reputation. Your domain's reputation is built on its sending history, spam complaint rates, engagement metrics (opens, clicks, replies), and proper email authentication protocols (SPF, DKIM, DMARC). This shift means that while a clean IP is still important, a strong domain reputation is now paramount for consistent inbox placement. You can learn more about this distinction by reviewing domain versus IP reputation.
Even with the increased focus on domain reputation, IP reputation still plays a role, particularly for new IPs that are being warmed up, or if an IP finds itself on a public blocklist (or blacklist). An IP on a major blocklist will severely impede deliverability, regardless of your domain's standing. That's why blocklist monitoring remains a crucial part of email deliverability management.
How DNS records relate to email sending
A subdomain's A record maps a hostname (like blog.yourdomain.com) to an IP address, typically for web traffic or other non-email services. This is distinct from the IP address used for sending emails. Email sending relies on MX records, which specify the mail servers responsible for accepting email on behalf of your domain.
When you send an email, the actual IP address from which the email originates is typically managed by your Email Service Provider (ESP) or your own mail server. This sending IP is linked to your domain through authentication records such as SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail). DMARC (Domain-based Message Authentication, Reporting & Conformance) then uses SPF and DKIM to verify the sender's legitimacy. A comprehensive understanding of DMARC, SPF, and DKIM is crucial.
Therefore, if you change a subdomain's A record to point to the same IP as your main domain's website, but you are still sending emails through your ESP's infrastructure (which uses its own set of IPs), this change will typically not alter the IP address your emails originate from. The IP address change you are making affects web services, not email transmission, unless the subdomain itself is configured as a direct mail server.
Understanding DNS records
When discussing IP changes and deliverability, it's vital to differentiate between the IP for web services (like your website) and the IP for email sending. Your A record for a subdomain typically points to its web server IP, not your email server. For email, MX, SPF, DKIM, and DMARC records are what guide email flow and authentication. Changing your web subdomain's A record won't affect your email flow unless you've specifically configured it to handle email sending directly.
When an IP change matters for email
If the subdomain in question is not used for sending email (e.g., it's a blog or application subdomain), changing its A record's IP to match your main domain's IP will have virtually no impact on your email deliverability. This is because email deliverability is primarily concerned with the IP address from which your mail server connects to recipient mail servers, and the reputation of the domain used in the MAIL FROM (or return-path) address.
However, if the subdomain is an email sending domain (e.g., mail.yourdomain.com) and you change its A record to a different IP, you must ensure that your email sending configuration (SPF, DKIM, DMARC) is updated to reflect this. But even in this case, the crucial factor is whether the actual IP from which your emails are sent has changed. If your ESP continues to send emails from the same IPs, an A record change for a subdomain's web IP won't directly affect email deliverability.
The only scenario where this specific change (subdomain A record IP to main domain IP) could affect email deliverability is if the new shared IP (the main domain's IP) is already associated with poor sending behavior or is on a blocklist. In such niche cases, linking to a problematic IP could inadvertently cause issues, even if it's just for a web subdomain. If your main domain's IP is on a blacklist (or blocklist), it might raise red flags for filters performing reverse DNS lookups, though this is less common for non-sending IPs.
It's generally a best practice to use subdomains for different email streams (e.g., transactional, marketing, internal communications). This strategy helps to isolate the reputation of each sending type. For example, if your marketing emails experience a high complaint rate, isolating them on a dedicated subdomain protects the reputation of your main domain, which might be used for critical business communications. This protective measure is more impactful than simply sharing a non-sending IP between a subdomain and main domain.
Maintaining email deliverability after infrastructure changes
Regardless of whether you change a subdomain's IP or not, maintaining excellent email deliverability hinges on consistent, good sending practices. This includes regularly cleaning your email lists to remove inactive or invalid addresses, segmenting your audience effectively, and crafting engaging content that recipients want to open and click. These factors contribute significantly to your sender reputation, which mail servers closely monitor.
Crucially, ensure all your sending domains and subdomains have properly configured email authentication. This includes SPF, DKIM, and DMARC records. These records verify that your emails are legitimate and prevent spoofing. Misconfigurations here can severely impact deliverability, regardless of your IP setup.
If you are changing your actual email sending IP (which is a different scenario from changing a web subdomain's A record), an IP warming process is essential. This involves gradually increasing your sending volume over time to build a positive reputation for the new IP. Neglecting this step can lead to immediate deliverability issues. For general guidelines, refer to Email sender guidelines.
Continuous monitoring of your deliverability metrics and sender reputation is also vital. Tools like Google Postmaster Tools can provide valuable insights into your domain and IP reputation, helping you identify and address potential issues before they severely impact your email campaigns. Regularly running an email deliverability test can also provide a snapshot of your current standing.
Views from the trenches
Best practices
Always maintain separate subdomains for different types of email (e.g., transactional, marketing) to isolate reputation risks and protect your main domain.
Ensure all DNS records (SPF, DKIM, DMARC) are correctly configured and updated for any domain or subdomain changes, as these directly impact authentication.
Consistently monitor your sender reputation and deliverability metrics through tools like Google Postmaster Tools and your ESP's reports.
Implement a gradual IP warming process if you are indeed changing your actual email sending IP, not just a web A record.
Common pitfalls
Confusing a web subdomain's IP address with the IP address used for sending email, leading to unnecessary worry or incorrect adjustments.
Failing to update SPF, DKIM, or DMARC records when making changes to your email sending infrastructure or domains.
Not warming up a new dedicated email sending IP, resulting in emails landing in spam folders or being rejected outright.
Ignoring signs of poor sender reputation, such as high bounce rates or spam complaints, assuming they are isolated incidents.
Expert tips
For most mailbox providers, domain reputation now outweighs IP reputation. Focus on consistently good sending practices and authentication.
A subdomain's A record pointing to a web IP is generally unrelated to email deliverability unless that IP is actively used for email sending.
If the shared IP has a poor reputation (e.g., on a blocklist), it could create issues even for non-sending subdomains, though this is a niche case.
The key factor is the IP from which emails are *actually* sent, which is often managed by your ESP and distinct from your web server IPs.
Marketer view
An expert from Email Geeks says they would be surprised if changing a subdomain's IP address for a non-email-sending purpose made any difference to email deliverability.
2023-09-07 - Email Geeks
Marketer view
An expert from Email Geeks explains that if a subdomain like mail.xyz.com is used as an outbound mail server, then changing its IP address would indeed alter the reputation for mail originating from it, requiring updates to SPF records and other authentication.
2023-09-07 - Email Geeks
Key takeaways
In summary, changing a subdomain's IP address to match your main domain's IP address will likely have minimal direct impact on your email deliverability, especially if the subdomain is not actively used for sending emails. The critical factor for email deliverability is the reputation of your email sending IP and, more importantly, your domain reputation.
Focus on maintaining clean sending practices, ensuring robust email authentication (SPF, DKIM, DMARC), and consistently monitoring your sender reputation. These are the pillars of strong email deliverability, far outweighing the impact of changing a non-sending subdomain's IP address.
Google and 
Yahoo (among others) place a much greater emphasis on domain reputation. Your domain's reputation is built on its sending history, spam complaint rates, engagement metrics (opens, clicks, replies), and proper email authentication protocols (SPF, DKIM, DMARC). This shift means that while a clean IP is still important, a strong domain reputation is now paramount for consistent inbox placement. You can learn more about this distinction by reviewing domain versus IP reputation.
