Summary
Changing a sending subdomain will indeed impact email deliverability and typically necessitates a new warm-up process for that specific subdomain. While the underlying IP address may remain the same, email service providers and mailbox providers assess sender reputation at both the IP and domain levels, including subdomains. This means that a new subdomain, even if part of a previously used root domain, must build its own sending history and reputation over time, similar to how a new dedicated IP would. The warm-up process for a new subdomain focuses on establishing positive sending metrics like low bounce rates and high engagement rates (opens, clicks), which are crucial for building trust with ISPs.
Key findings
- Subdomain reputation: Each subdomain (e.g., email.yourdomain.com) carries its own distinct reputation, independent of the root domain or other subdomains you might be using.
- Warm-up necessity: A new subdomain almost always requires a warm-up, even if it uses an existing, warmed IP address. This is because mailbox providers build reputation for the specific sending domain, not just the IP. Mailgun, for instance, highlights that new domains, including subdomains, will most likely need to be warmed up.
- Deliverability impact: Changing the sending subdomain directly impacts deliverability because recipients' email systems (ISPs) need to recognize and trust the new sending identity.
- Bounce and From domains: Both the From domain (what recipients see) and the Return-Path (bounce) domain contribute to sender reputation and are tied to the subdomain in use.
- ESPs and subdomain configuration: Some ESPs, particularly with full Sender Authentication Packages (SAPs), may impose limitations on using the same domain across multiple platforms due to DNS hosting or DKIM configurations. This often leads to using distinct subdomains for different ESPs, necessitating individual warm-ups. For more details on this, see best practices for migrating ESPs.
Key considerations
- Gradual volume increase: Even if less arduous than IP warming, a gradual increase in sending volume from the new subdomain is advisable to build trust with ISPs and avoid triggering spam filters.
- Engaged audience focus: Start by sending to your most engaged subscribers with the new subdomain. This helps generate positive engagement signals, which are vital for establishing a good reputation.
- Monitoring: Closely monitor deliverability metrics such as open rates, click-through rates, bounce rates, and spam complaint rates for the new subdomain to quickly identify and address any issues. Using domain warming best practices is essential.
- DNS records: Ensure that all necessary DNS records (SPF, DKIM, DMARC) are correctly configured for the new subdomain before sending any emails.
What email marketers say
Email marketers often find themselves in situations where changing a sending subdomain becomes necessary, whether due to ESP migration, rebranding, or segmenting email types. Their experiences highlight that while the IP address might stay the same, the subdomain itself acts as a distinct identity in the eyes of mailbox providers. This distinct identity requires a new period of reputation building, often referred to as 'domain warming,' even if it is not as intensive as IP warming.
Key opinions
- Domain change impact: Many marketers confirm that changing the sending domain, even just a subdomain, will impact deliverability.
- Subdomain warm-up needed: The consensus is that a new subdomain will need warming, though it might be less rigorous than a full IP warm-up. This is echoed by a marketer on Salesforce's Trailhead community who inquired about warming a new email sending subdomain even on a shared IP.
- Separate reputations: Marketers frequently emphasize that subdomains build individual reputations, meaning positive reputation from one subdomain does not automatically transfer to another, even under the same root domain.
- Return-path considerations: The return-path (bounce) domain often changes with the sending subdomain, which also contributes to the sending identity that needs to be established. See best practices for changing your return-path domain.
- Multi-ESP domain usage: While some ESPs allow the same domain (e.g., your root domain for From: header) to be used concurrently across multiple platforms, dedicated subdomain setups for each ESP are common, each requiring its own warm-up.
Key considerations
- Strategic planning: Plan any subdomain changes carefully, considering the potential impact on deliverability and allocating time for a warm-up period. This applies to domain rebranding as well.
- Engaged segments first: When warming a new subdomain, prioritize sending to your most active subscribers to establish positive engagement metrics early on.
- Volume control: Gradually increase email volume sent from the new subdomain, even if it's on an already warmed IP, to prevent sudden spikes that could trigger spam filters.
- Aligning authentication: Ensure all email authentication protocols (SPF, DKIM, DMARC) are properly configured and aligned for the new subdomain to maintain sender authenticity.
Marketer view
Marketer from Email Geeks states that changing the domain the messages are coming from will indeed impact deliverability, implying a warm-up is necessary.
Marketer view
A marketer from Mailbluster indicates that if one chooses to proceed with a new email domain, which includes subdomains, implementing a proper warm-up strategy is essential, starting with a small volume.
What the experts say
Email experts agree that a subdomain change, even when keeping the same IP, is a significant event for email deliverability. They emphasize that domain reputation is a critical factor independent of IP reputation, and switching subdomains essentially means introducing a new sending identity to mailbox providers. This new identity needs to earn its trust, which is achieved through a deliberate warm-up process focused on positive engagement and low complaint rates.
Key opinions
- Domain warming matters: Experts confirm that domain warming is indeed important, though generally less arduous than IP warming.
- Subdomain reputation is separate: Each subdomain builds its own reputation. If you move from sub1.domain.com to sub2.domain.com, sub2 starts with a fresh reputation.
- Restrict initial sending: To prevent issues, it is recommended to initially restrict sending from a new subdomain to only the most engaged or best performing segments of your audience. For more about this, check our article on domain warming effectiveness.
- SFMC SAP limitations: Some ESPs, like Salesforce Marketing Cloud (SFMC) with its Sender Authentication Package (SAP), require them to host DNS for the SAP domain, which can limit the ability to use that exact domain for multi-ESP sending with multi-DKIM setups.
- Workarounds exist: Experts describe strategies, such as setting up a primary SAP domain (e.g., email.yourdomain.com) and also configuring the root domain (yourdomain.com) as a private domain with DKIM to enable sending from the root while maintaining alignment via the bounce domain (e.g., bounce.email.yourdomain.com). This allows flexibility and concurrent sending across multiple ESPs for the root domain if correctly set up.
Key considerations
- Patience and consistency: Building subdomain reputation takes time and consistent positive sending behavior.
- Technical configuration: Proper setup of SPF, DKIM, and DMARC records for the new subdomain is non-negotiable for successful deliverability.
- Engagement signals: Focus on content that drives opens and clicks to rapidly improve the new subdomain's reputation.
- Monitor blocklists: Even with warming, monitor for any signs of being added to a blacklist or blocklist, as new domains are sometimes more susceptible. You can use our blocklist checker for this.
Expert view
Expert from Email Geeks indicates that domain warming does matter, although it is not as arduous as IP warming. They suggest introducing the switch at low volume and gradually building it up to aid deliverability.
Expert view
An expert from Spam Resource clarifies that even if the IP is known, a new domain or subdomain still requires warming. ISPs maintain reputation data specific to the domain
What the documentation says
Official documentation and guides from various email service providers and industry bodies consistently emphasize the importance of domain reputation alongside IP reputation. When a sending subdomain is changed, it's effectively a new sender identity from the perspective of mailbox providers. This new identity, even if sharing the same root domain or IP, must establish its own sending history and credibility. Documentation outlines that this process involves proper DNS configuration and a strategic ramp-up of sending volume to avoid deliverability pitfalls.
Key findings
- Domain reputation importance: Documentation often highlights that domain reputation plays a crucial role in deliverability, sometimes even more so than IP reputation, especially for shared IPs.
- Subdomain as new entity: New subdomains are treated as distinct sending entities that require their own warm-up period to establish trust.
- Warm-up process: The warming process for a new domain or subdomain involves gradually increasing sending volume while maintaining high engagement rates and low complaint rates. Google Postmaster Tools, for example, heavily relies on domain reputation metrics to assess sender quality. You can understand this further with our guide to Google Postmaster Tools domain reputation.
- Authentication setup: Proper configuration of SPF, DKIM, and DMARC for the new subdomain is fundamental for authentication and deliverability. Learn more about DMARC, SPF, and DKIM.
- Dedicated sending domains: Documentation (e.g., HighLevel's Email Sending Guide) often promotes setting up a dedicated email sending domain (which could be a subdomain) to gain full control over reputation and deliverability.
Key considerations
- Separate reputation management: Treat each new subdomain as an entity that needs its own reputation management strategy, including its own warm-up plan.
- Monitor performance: Leverage tools like Google Postmaster Tools to monitor the reputation of the new subdomain specifically.
- Impact on other subdomains: While reputations are largely separate, a severe issue with one subdomain can, in rare cases, spill over and affect the root domain or other subdomains, especially if abusive practices are detected.
- Structured warm-up: Follow structured warm-up schedules provided by ESPs or industry guides to build trust gradually with mailbox providers.
Technical article
Documentation from Mailgun states that with a new domain, whether it's a subdomain or a root domain, you'll most likely need to warm up the domain itself, and this is done almost the same way as an IP warm-up.
Technical article
Documentation from EmailLabs outlines that warming up involves ensuring that domains or subdomains are correctly configured and slowly added into the sending flow, identifying this as a best practice.
Related resources
12 resources
Related pages
When switching to a new subdomain for email, what warm-up process is required?
How do you warm up a new sending domain on an existing warmed IP address?
What are the best practices for migrating ESPs with subdomain and IP warmups?
What is the email deliverability impact of domain rebranding when keeping existing warm IPs?
What are the best practices for changing an email's return-path domain, especially regarding DKIM and warm-up?
Will using a subdomain for different email types affect my primary domain's reputation?
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