Will changing the sending subdomain impact email deliverability and require a new warm-up process?
Matthew Whittaker
Co-founder & CTO, Suped
Published 8 Jul 2025
Updated 19 Aug 2025
7 min read
Many email senders wonder if changing their sending subdomain will necessitate a new warm-up process and impact their overall email deliverability. It is a common question, especially when migrating to a new email service provider (ESP) or restructuring email sending practices. The short answer is yes, changing a sending subdomain typically impacts deliverability and requires a new warm-up, even if your underlying IP address remains the same.
This might seem counterintuitive since IP warm-up is frequently discussed, but domain reputation plays a significant role. Mailbox providers, such as Google and Microsoft, assess reputation at both the IP and domain levels. When you introduce a new subdomain, it effectively acts as a fresh sending identity that hasn't built trust yet, regardless of the IP it's associated with.
The impact of domain reputation
When you change your sending subdomain, you are essentially introducing a new identity to mailbox providers. While your dedicated IP address might have a good reputation from previous sending, that reputation is primarily tied to the specific domain or subdomain that was used. A new subdomain lacks this historical context, even if it's still part of your main domain.
This is because domain reputation is a critical factor in deliverability. It is built over time through consistent sending practices, low spam complaints, high engagement, and proper email authentication. A fresh subdomain doesn't inherit this established trust automatically. For example, if you send from email.yourdomain.com and switch to news.yourdomain.com, mailbox providers will view news.yourdomain.com as a new sender.
Even if your hello.com domain has a strong overall reputation, each subdomain builds its own specific sender reputation. This independent reputation is crucial for avoiding spam folders and ensuring your emails reach the inbox. I've often seen situations where a poorly managed subdomain can even indirectly affect the main domain's reputation, reinforcing the need for careful management of each sending identity.
The necessity of subdomain warm-up
While IP warming is focused on building trust for a specific IP address, domain warming (or subdomain warming) serves a similar purpose for your sending domain. The process involves gradually increasing the volume of emails sent from the new subdomain over time. This slow and deliberate approach demonstrates to mailbox providers that you are a legitimate sender and not a spammer.
Neglecting to warm up a new subdomain, even when using an already warmed IP, can lead to serious deliverability issues. Mailbox providers might flag sudden spikes in volume from an unknown (new) subdomain as suspicious, resulting in emails being routed to the spam folder or even being outright blocked. This is particularly true if you intend to send large volumes of mail. You can learn more about how to warm up a new subdomain for email sending in our dedicated guide.
The warming process for a subdomain is typically less arduous than for a new IP, but it is still crucial. The key is to build a positive sending history associated with that specific subdomain. This involves sending emails to highly engaged subscribers first, monitoring your sender reputation metrics, and gradually expanding your sending volume and audience. Our article on what warm-up process is required when switching to a new subdomain provides more details.
Authentication and technical setup
When you switch to a new sending subdomain, you must ensure that your email authentication records are correctly configured for that specific subdomain. This includes SPF, DKIM, and DMARC. These DNS records tell receiving mail servers that your emails are legitimate and authorized to be sent from your domain.
I've seen issues arise when these records aren't set up correctly for the new subdomain, even if they were perfect for the old one. This can lead to authentication failures, which significantly impact deliverability and can land your emails directly in the spam folder. Specifically, ensuring your return-path domain (often derived from your sending subdomain) is correctly aligned is critical.
Beyond deliverability, changing your sending subdomain might also affect other aspects of your email program, such as image hosting and link wrapping. If your ESP uses your subdomain for a Sender Authentication Package (SAP), then elements like https://img.yourdomain.com for images or https://click.yourdomain.com for tracking links will also need to be updated and managed under the new subdomain.
DNS records to verify
SPF (Sender Policy Framework): Authorizes specific IP addresses to send mail on behalf of your subdomain.
DKIM (DomainKeys Identified Mail): Provides a cryptographic signature to verify the sender and ensure message integrity.
DMARC (Domain-based Message Authentication, Reporting & Conformance): Specifies how receiving mail servers should handle emails that fail SPF or DKIM authentication.
Strategies for a smooth transition
To ensure a smooth transition and maintain strong deliverability, I recommend a phased approach when changing your sending subdomain. Avoid making an abrupt switch, as this can trigger spam filters and lead to poor inbox placement.
Begin by slowly introducing the new subdomain, sending small volumes of email to your most engaged subscribers. Over several days or weeks, gradually increase the sending volume from the new subdomain while slowly phasing out the old one. This allows mailbox providers to recognize and trust your new sending identity. Our guide on best practices for warming up a new subdomain provides a detailed schedule.
Monitoring your deliverability metrics closely during this period is essential. Pay attention to inbox placement rates, bounce rates, and complaint rates. If you see any red flags, slow down your sending from the new subdomain and re-evaluate your strategy. It's also wise to keep the old subdomain active for a period, perhaps for transactional emails or lower-priority sends, until the new one is fully warmed.
Old subdomain
Maintain active reputation and continue sending at previous volumes for a grace period. This ensures continuity and avoids abrupt changes that could harm your overall sending domain.
New subdomain
Implement a gradual warm-up schedule, starting with low volumes to highly engaged segments. This builds trust with mailbox providers over time. You might also explore strategies for warming up domains specifically.
Views from the trenches
Best practices
Start warming up your new subdomain by sending to your most engaged subscribers first, gradually increasing volume.
Ensure all DNS records (SPF, DKIM, DMARC) are correctly configured for the new subdomain.
Monitor your deliverability metrics closely during the warm-up period for any signs of trouble.
Segment your audience and introduce the new subdomain slowly across different segments.
Common pitfalls
Abruptly switching all email volume to a new subdomain, which triggers spam filters.
Failing to update all necessary DNS records for the new subdomain.
Not monitoring engagement and bounce rates during the warm-up, leading to unnoticed issues.
Sending to unengaged or old lists from a new subdomain, harming its initial reputation.
Expert tips
If possible, overlap sending from both the old and new subdomains during transition.
Use Google Postmaster Tools and other monitoring platforms to track your new subdomain's reputation.
Consider segmenting your email types (e.g., transactional, marketing) across different subdomains.
Engage in active list hygiene to ensure high-quality recipients for warming.
Marketer view
Marketer from Email Geeks says that changing the domain your messages are coming from will require a new warm-up.
2022-05-19 - Email Geeks
Expert view
Expert from Email Geeks says if a domain has been used elsewhere, warm-up is about filters associating the domain and IP address. If it's a new domain, slow warm-up is needed.
2022-05-19 - Email Geeks
Navigating subdomain changes
In conclusion, changing your email sending subdomain, even if the IP address remains the same, does impact email deliverability and necessitates a new warm-up process. Subdomains develop their own distinct sender reputation that is independent of the root domain or the IP address. Therefore, treating a new subdomain as a fresh sender identity and warming it up appropriately is crucial for maintaining optimal inbox placement.
By diligently setting up all necessary authentication records and following a systematic warm-up plan, you can successfully transition to a new subdomain without severely disrupting your email program. Remember that consistency and careful monitoring are your best allies in navigating any changes to your email infrastructure and safeguarding your sender reputation.
Google and 
Microsoft, assess reputation at both the IP and domain levels. When you introduce a new subdomain, it effectively acts as a fresh sending identity that hasn't built trust yet, regardless of the IP it's associated with.
