How does changing ESPs and domains affect sender reputation and email deliverability?
Michael Ko
Co-founder & CEO, Suped
Published 30 Jul 2025
Updated 16 Aug 2025
9 min read
Changing email service providers (ESPs) or domains can feel like a significant leap, often accompanied by questions about how it will impact your hard-earned sender reputation and, consequently, your email deliverability. It's a valid concern, as mailbox providers (MBPs) meticulously track sending behavior to determine if your emails should land in the inbox or be flagged as spam.
The short answer is yes, such changes will affect your sender reputation, at least in the short term. The extent of this impact, and how quickly you recover, largely depends on your strategy. This is because your reputation is tied not only to the sending IP address but also heavily to your domain.
Understanding sender reputation
Your sender reputation is a critical score that MBPs use to assess the trustworthiness of your emails. This score is built over time, based on various factors like spam complaint rates, bounce rates, engagement (opens and clicks), and how consistently you send emails. A strong reputation signals to MBPs that your emails are legitimate and desired by recipients, leading to better inbox placement. Conversely, a poor reputation can lead to emails being sent to the spam folder or blocked outright.
Traditionally, IP reputation was the primary factor in deliverability. However, with the widespread adoption of shared IP pools by ESPs and the increasing sophistication of spam filters, domain reputation has become even more crucial. Your domain (e.g., example.com) is unique to your brand, allowing MBPs to track your sending history and recipient interactions directly associated with your brand identity, regardless of the underlying IP address used by your ESP. This means your email sending practices directly impact your domain reputation.
When you switch ESPs, you often get a new set of IP addresses, which requires a new IP warming process to build trust with MBPs. Even if you retain your existing sending domain, the change in the underlying sending infrastructure (the new IPs) introduces an element of newness that filters will scrutinize. However, your domain's existing positive reputation can help to mitigate some of the initial impact, as it acts as a familiar and trusted identifier for MBPs.
The dual impact of ESP and domain changes
The challenge intensifies when you decide to change both your ESP and your primary sending domain simultaneously. This introduces a double layer of 'newness' to MBPs. They will see a new IP reputation being built and a new domain or subdomain attempting to establish its own trustworthiness. This scenario significantly increases the degree of change that filters need to process, potentially leading to a longer period of reduced deliverability while your new setup proves itself.
While your domain reputation is sticky and will follow you, even if you switch IPs or email service providers, a new domain starts with a neutral, or even suspicious, reputation. MBPs view email from a new domain as inherently questionable until it establishes a positive sending history. This means you will effectively be starting fresh with your domain's reputation, requiring a dedicated warm-up strategy similar to that for new IPs. You can't avoid a negative domain reputation by simply switching ESPs or using different sender addresses, as the core reputation is tied to your domain.
One common question is whether you should keep your existing domain when changing ESPs. If you have a strong domain reputation, it's generally advisable to retain it. You can often configure your new ESP to send using your existing domain, though this requires careful DNS record updates (SPF, DKIM, DMARC) to ensure continuity and proper authentication. This blended approach allows you to leverage your existing domain's trust while warming up new IPs associated with your new ESP.
If you do decide to switch your domain along with your ESP, it means enduring a period of potential deliverability challenges as you build a new reputation from scratch. However, if your existing domain has a poor reputation, a fresh start with a new domain might be necessary to escape past issues. The key is to approach either scenario with a clear strategy and a robust warming plan.
Keeping your existing domain
Leverage existing trust: MBPs recognize your established domain, potentially easing the transition.
Smoother migration: Less impact on recipient recognition and engagement metrics.
Complex setup: Requires careful management of DNS records (SPF, DKIM, DMARC) to authenticate emails from the new ESP.
Changing to a new domain
Fresh start: Beneficial if your old domain had a poor reputation or has been blocklisted.
Reputation building: Requires a complete domain warming process, which can be time-consuming.
Recipient confusion: Recipients may not immediately recognize the new domain, leading to lower engagement or spam complaints.
Strategic domain management for deliverability
A critical aspect of domain management is whether to use your main organizational domain or subdomains for email sending. While you can use your primary domain, creating dedicated subdomains (e.g., mail.yourdomain.com, alerts.yourdomain.com) for different email types is often a best practice. This helps isolate the reputation of various sending streams. For example, if your marketing emails experience a dip in deliverability or land on a blocklist, your transactional emails (like password resets or order confirmations) sent from a separate subdomain are less likely to be affected.
It is also crucial to avoid using entirely separate or 'cousin' domains that are unrelated to your main brand (e.g., yourbrand-updates.com). This practice can confuse recipients, making it easier for phishers to impersonate your brand using similar-looking domains. Furthermore, some MBPs may view this as a 'snowshoeing' tactic to bypass filters, which can result in penalties not just for the 'cousin' domain but potentially the entire brand. Stick to subdomains of your main domain for consistent branding and security.
If you currently use one domain or subdomain for all your email sending and are considering separating them, it is a sound strategy from a deliverability perspective. For instance, you could use orders@brand.com for transactional emails and marketing@e.brand.com for promotional content. This separation ensures that even if your marketing efforts hit a snag, the deliverability of your critical transactional emails remains largely unaffected. However, note that parent domain reputation can still influence subdomains. Additionally, it’s worth reviewing the M3AAWG document on sending domain best current practices.
Isolate sending types: Use separate subdomains for transactional, marketing, and potentially even cold outreach emails to protect your core reputation.
Consolidate branding: Always use subdomains of your primary brand domain to maintain consistency and trust, avoiding 'cousin' domains.
Ensure proper authentication: Verify SPF, DKIM, and DMARC records are correctly configured for all sending domains and subdomains.
Strategic considerations for migration
Whether you perform a hard cut or a gradual transition when moving ESPs and domains, meticulous planning is essential. A gradual transition, using a new subdomain with your new ESP while keeping the old ESP active for a period, allows for a smoother warm-up process. This blended approach enables you to slowly shift volume to the new platform while your existing setup handles any lingering campaigns or unsubscribe requests.
Key technical preparations involve updating your DNS records. Ensure your SPF record includes the new ESP's sending IP addresses or mechanisms. Set up DKIM with unique selectors for your new ESP, allowing both old and new systems to sign emails during a transition period. Most importantly, configure DMARC records to align with your new sending sources. Proper SPF, DKIM, and DMARC setup is foundational for maintaining domain reputation.
Also, pay close attention to the `List-Unsubscribe` header. If your current domain is used in this header, ensure that the new ESP can process these unsubscription requests, especially for automated campaigns that might still be in flight. Maintaining valid unsubscribe functionality is critical for compliance and positive sender reputation. Don't forget to verify all older or automated campaigns are completed before making any hard cuts to MX records or previous ESP services.
Views from the trenches
Best practices
Ensure your SPF record is updated with all new ESP IPs or mechanisms to maintain proper authentication.
Implement DKIM with unique selectors for your new ESP, allowing a dual-signing period if transitioning gradually.
Configure DMARC records to align with your new sending sources, monitoring reports closely during the transition.
Separate transactional and marketing emails onto different subdomains to isolate reputation risks.
Prioritize keeping your main sending domain if it has a strong existing reputation to leverage established trust.
Common pitfalls
Attempting a hard cut without proper DNS updates can lead to significant deliverability drops and email rejections.
Not warming up new IPs or domains gradually can trigger spam filters and result in blocklistings (blacklists).
Failing to maintain unsubscribe functionality from the old ESP, especially for in-flight campaigns, can lead to compliance issues.
Using completely unrelated 'cousin' domains can confuse recipients and be seen as a 'snowshoeing' tactic by MBPs.
Underestimating the time and effort required for reputation building on new sending infrastructure.
Expert tips
Consider a blended transition: gradually shift email volume to the new ESP while maintaining the old one temporarily.
For transactional emails, consider a dedicated subdomain (e.g., t.yourdomain.com) for improved isolation and deliverability.
Double DKIM signing with old and new domains simultaneously can help leverage existing reputation during a domain change.
Engage directly with your new ESP to understand their specific migration and warming recommendations.
Regularly monitor your domain and IP reputation using tools like Google Postmaster Tools throughout the migration.
Marketer view
Marketer from Email Geeks says that changing domains at the same time as switching ESPs increases the degree of change, prolonging the time filters need to reacquaint themselves with the sender. It is advised to change ESP first, wait a month or two for everything to stabilize, and then change the domain.
2022-02-03 - Email Geeks
Marketer view
Marketer from Email Geeks says that if you are changing your sending setup to fix a deliverability problem, simply changing ESPs or domains will not fix the issue in the long term. The underlying sending practices must be addressed.
2022-02-03 - Email Geeks
Key takeaways for smooth transitions
Changing ESPs and domains is a significant undertaking that directly impacts your sender reputation and email deliverability. While it introduces new elements that MBPs will scrutinize, strategic planning can minimize negative effects. The primary takeaway is that your domain reputation is paramount, even more so than IP reputation in today's landscape.
By understanding how these changes affect your sending identity, carefully planning your migration, correctly configuring your DNS records, and diligently warming up any new IPs or domains, you can ensure a smooth transition and maintain (or even improve) your email deliverability. Remember, consistency and adherence to best practices are your strongest allies in building and preserving a robust sender reputation.
