Should I use subdomains or a single domain for email marketing after a brand merger?
Michael Ko
Co-founder & CEO, Suped
Published 27 Apr 2025
Updated 16 Aug 2025
7 min read
Navigating email marketing strategy after a brand merger presents unique challenges, particularly when deciding on your sending domain structure. The fundamental question is whether to consolidate all email sending under a single new brand domain or to maintain distinct identities, often through subdomains, especially if you previously managed separate country-specific domains.
I’ve seen firsthand how crucial this decision can be for deliverability. While a single domain might simplify branding, using subdomains offers distinct advantages, particularly in managing sender reputation and adapting to varied regional email engagement patterns. The goal is to ensure your emails consistently reach the inbox, avoiding spam folders, while also aligning with the new brand identity.
Managing sender reputation across regions
One of the primary reasons to consider subdomains, even after consolidating web properties, is to preserve and manage sender reputation. Email Service Providers (ISPs) like Google and Microsoft assign a reputation score to the sending domain, which heavily influences whether emails land in the inbox or the spam folder. If one regional marketing team has poor sending practices (e.g., sending to unengaged lists, high bounce rates), it can negatively impact the reputation of the entire domain. Subdomains act as firewalls, isolating the reputation of different email streams.
For brands with a global presence, different markets often have unique subscriber behaviors and cultural norms that affect email engagement. For instance, what resonates well in one country might not in another, leading to varying open rates, click-through rates, and complaint rates. By using subdomains like email-pt.new-brand-name.com or email-es.new-brand-name.com, you can monitor and manage the sender reputation for each region independently. This granularity is particularly useful if some markets had a history of lower reputation or if you're integrating newly acquired assets with questionable sending histories. Isolating these streams ensures that a deliverability issue in one market doesn't cascade and affect your entire global email program.
It’s also important to note that while separating marketing and transactional emails is a common best practice, applying this at a regional level with subdomains takes it a step further. This approach provides a clear view into the performance of each regional email program through tools like Google Postmaster Tools. It allows for targeted adjustments and remediation efforts if a specific market faces deliverability challenges, rather than a blanket approach that might not be necessary or effective for all regions.
Balancing branding with deliverability
A brand merger often aims for a unified brand identity. This typically means consolidating web properties under a single, new brand domain. The challenge then becomes how to reconcile this unified web presence with a potentially segmented email sending strategy. While a single new-brand-name.com email domain might seem ideal for consistent branding, it's essential to weigh the deliverability implications.
Using subdomains still allows you to align with the new brand. For instance, instead of brand-name.pt, you would use email-pt.new-brand-name.com. This retains the association with the primary brand while providing the necessary segmentation for email reputation. For European B2C customers, seeing a local identifier (e.g., pt in the subdomain) can create a sense of familiarity and trust, potentially boosting engagement. This is a subtle but effective way to balance global branding with local relevance.
Single primary domain
Pros: Simplified branding and domain management. All emails appear to come from one unified entity. Potential for aggregated email volume to build a strong overall reputation, especially for smaller markets. May simplify authentication setups.
Cons: A deliverability issue (e.g., a blocklist or blacklist listing) in one region affects all email sending from the main domain globally. Less granular reputation monitoring and troubleshooting.
Subdomains per market
Pros: Isolated sender reputation, protecting the overall brand deliverability from localized issues. Easier to identify and resolve regional deliverability problems. Allows for tailored sender branding (e.g., email-pt).
Cons: More complex initial setup and ongoing management of DNS records and authentication for multiple subdomains. Smaller markets may struggle to build sufficient volume to establish strong individual subdomain reputations, as discussed by Allegrow.
For the new unified brand, a blended approach might be effective. The main website consolidates under new-brand-name.com, with regional content delivered via URL paths (e.g., new-brand-name.com/es-es). Email sending, however, could retain the subdomain structure to allow for separate reputation management and localized From: addresses if desired. This way, you get the best of both worlds: centralized branding for the website and localized, protected email sending.
Technical infrastructure and monitoring
Regardless of your chosen strategy, proper technical setup is paramount. This includes configuring SPF, DKIM, and DMARC records for each sending domain or subdomain. These authentication protocols verify that your emails are legitimate and prevent spoofing, which is vital for maintaining a good sender reputation. After a merger, updating these records for all affected domains is a critical, often complex, task.
When using an Email Service Provider (ESP) or Marketing Automation Platform (MAP), be aware of how their domain setup works. Some platforms, like Mailgun (as mentioned in a related discussion), might use a single domain field that determines the domains for From:, Return-Path, and DKIM d= headers. This means you might not have the flexibility to use a primary domain for branding and a different subdomain for the technical sending domain. Understanding these limitations is key to choosing the right strategy.
Monitoring your domain's health after a merger is critical. Google Postmaster Tools provides valuable insights into your domain's reputation, including spam rates, IP reputation, and DMARC authentication status. If you opt for separate subdomains per market, you can add each subdomain to Google Postmaster Tools for individual monitoring. This allows you to identify and address deliverability issues at a granular level, helping you recover reputation more effectively.
Example SPF record for multiple subdomains
For each subdomain you use for email sending, you'll need a specific SPF record. While the primary domain might have its own SPF, subdomains need their own entries to correctly authorize sending servers.
SPF record for email-pt.new-brand-name.comDNS
v=spf1 include:_spf.mailgun.org ~all
SPF record for email-es.new-brand-name.comDNS
v=spf1 include:_spf.mailgun.org ~all
This granular monitoring allows you to quickly identify if a specific market is struggling with deliverability and apply targeted solutions without affecting the overall brand. For example, if email-es.new-brand-name.com shows a high spam rate in Google Postmaster Tools, you can investigate that specific market's list hygiene, content, or sending frequency. This level of insight is invaluable for proactive email deliverability management, especially when dealing with diverse audiences post-merger.
The strategic choice
After a brand merger, the optimal domain strategy for email marketing boils down to careful consideration of reputation management versus branding consistency and operational simplicity. While a single domain might appear to be the straightforward choice for unified branding, the benefits of subdomains in isolating sender reputation often outweigh the added complexity, especially for global brands with diverse audiences.
By maintaining distinct subdomains for each market, you gain the ability to monitor and manage each region's email performance independently. This helps to safeguard your overall brand reputation from localized deliverability issues. It also provides the flexibility to adapt your email strategy to the unique cultural nuances and engagement patterns of different audiences, ultimately leading to better inbox placement and campaign results across your new, unified brand.
Views from the trenches
Best practices
Isolate different email streams, especially marketing vs. transactional, using distinct subdomains to protect your main domain's reputation.
Leverage Google Postmaster Tools to monitor subdomain reputation metrics separately, even if your main domain consolidates analytics.
Ensure all DNS records (SPF, DKIM, DMARC) are correctly configured for each sending subdomain to ensure proper authentication.
Consider cultural nuances and local preferences, as these can impact recipient engagement and, consequently, sender reputation.
Common pitfalls
Underestimating the time and effort required for warming up new subdomains or domains after a brand merger.
Failing to implement DMARC with a policy of 'quarantine' or 'reject' to protect against unauthorized use of your merged brand's domains.
Over-segmenting email sending into too many low-volume subdomains, which can hinder the ability to build a robust sending reputation.
Neglecting to monitor domain and IP blocklists (blacklists) across all new and old domains post-merger, leading to deliverability issues.
Expert tips
A consolidated approach with subdomains under a single new brand domain can simplify management while allowing for some reputation isolation.
Even with a single main domain, careful segmentation of recipient lists and content tailoring for different regions remains crucial.
Test deliverability thoroughly across all affected regions and ISPs before migrating all email traffic to new domain structures.
If forced to a single primary domain, explore using different 'Friendly From' names to maintain regional branding recognition.
Marketer view
Marketer from Email Geeks says: Using subdomains for different countries can cause issues if one country's marketing team is not careful, as a DBL listing on a subdomain can quickly escalate to the organizational domain.
2021-09-13 - Email Geeks
Expert view
Expert from Email Geeks says: It is generally recommended to keep everything under the same organizational domain, possibly with subdomains for different regions, to build reputation through aggregated volume and engagement.
2021-09-13 - Email Geeks
Final considerations
The decision to use subdomains or a single domain after a brand merger requires a comprehensive understanding of your email program's scale, regional audience behavior, and the capabilities of your sending platform. While consolidating under a single domain simplifies branding, a subdomain strategy offers a more robust framework for managing sender reputation and mitigating risks across diverse markets.
By carefully weighing these factors and implementing the necessary technical configurations, you can ensure that your merged brand's email communications are both on-brand and highly deliverable, reaching your customers effectively worldwide.
