Postmaster Tools V2 and Gmail Compliance: The Case for Subdomains in Email Deliverability

The recent updates to Gmail's Postmaster Tools V2 have sparked renewed conversations on the compliance requirements for organizational domains and their subdomains. While the rollout and subsequent rollback of some changes initially caused ripples in the email deliverability community, I can now confirm that the updates have been rolled out again, based on my latest observations (as seen screenshot below). This reinforces the critical importance of the interconnected reputation of organizational domains and their subdomains.

In this article, I’ll explore the nuances of Gmail compliance and why the use of subdomains on campaigns continues to be an important tool in maintaining and improving email deliverability. I’ll also share insights from testing and observations that reveal how Google evaluates compliance at both the organizational and subdomain levels.

Gmail Compliance: Organizational Domains vs. Subdomains

One of the key revelations from Gmail's Postmaster Tools V2 is how compliance is assessed for organizational domains and subdomains. Subdomains, often used for segmentation and campaign management, are not entirely independent. Instead, they are directly tied to their root domain's reputation.

Here’s the key takeaway: the reputation and compliance of the organizational domain are foundational. Even if a subdomain meets all technical requirements and compliance benchmarks, its deliverability can still be affected by issues at the root domain level. This reinforces the importance of a holistic domain management strategy.

Why Subdomains Are Still Key to Email Deliverability

Despite their dependency on the root domain, subdomains remain invaluable for email marketers. When used effectively, they allow for:

1. Campaign Segmentation: Subdomains enable senders to isolate specific campaigns, mitigating risks of negative engagement (e.g., spam complaints) from affecting other streams.
2. Reputation Management: Subdomains act as a buffer, protecting the root domain from issues tied to certain email types or campaigns.
3. Targeted Strategies: By assigning subdomains to different email streams (e.g., marketing, transactional, or customer support), senders can better align with recipient expectations.

These benefits, however, are contingent on the health and compliance of the root domain. Without resolving issues like failing to honor unsubscribe requests or implementing one-click unsubscribe links, even the most well-configured subdomain could face challenges.

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Insights from Gmail’s Updated Compliance Standards

Testing and observations with Gmail's Postmaster Tools V2 reveal that compliance requirements are not just suggestions, they are pivotal to maintaining a good reputation with Gmail. Some highlights include:

• One-Click Unsubscribe Is Essential. Gmail evaluates whether senders implement this feature, and non-compliance can negatively affect domain reputation.
• Unsubscribe Requests Must Be Honored. Failing to respect recipient preferences will undermine your deliverability and reputation.
• Subdomain Success Depends on Root Domain Compliance. Even the most perfectly configured subdomain can be hindered by compliance failures at the organizational level.

These findings reveal the need for email senders to prioritize compliance across all domains, starting with the root domain.

Practical Steps for Improving Domain Compliance

To navigate Gmail’s compliance standards and optimize deliverability, email senders should focus on these strategies:

1. Audit Your Organizational Domain. Use Gmail Postmaster Tools to assess compliance and identify issues at the root domain level.
2. Strengthen Unsubscribe Mechanisms. Ensure that your unsubscribe links are easy to find and use. Test their functionality regularly.
3. Monitor Subdomain Activity. While subdomains are valuable for segmentation, their performance should be continuously monitored to avoid cross-contamination with the root domain, make sure you add your subdomains to Google Postmaster Tools separately.
4. Educate Your Team. Make sure that people in your organisation that sends mass emails understand the interconnected nature of subdomains and root domains.

The Bigger Picture: Subdomains and Gmail Compliance

The recent Gmail compliance updates emphasize this crucial point: subdomains cannot be isolated from their organizational domain. While they are essential tools for segmentation and deliverability, their success depends on the foundational health of the root domain.

As email marketers, it’s our responsibility to adopt a proactive, holistic approach to domain management. By addressing compliance issues at both the organizational and subdomain levels, we can build stronger reputations, improve deliverability, and navigate Gmail’s evolving standards with confidence.

Once you have ensured the core domain's health and security, your next step is to strategically implement subdomains for improved traffic segmentation. Below are key areas where separate subdomains can be beneficial:

• Email Marketing Campaigns – Use a dedicated subdomain for regular email subscriber communications (e.g., @hello.companydomain.com).
• Event-Specific Campaigns – Implement temporary subdomains for managing high-volume, one-off campaigns, protecting the root domain from potential spikes in email activity (e.g., @event.companydomain.com).
• Sales Communications – Assign a separate subdomain for the sales team to engage with prospects and manage their pipeline effectively (e.g., mail.companydomain.com).
• Regional-Specific Outreach – For businesses with global operations, localized subdomains can enhance regional communications (e.g., @asia.companydomain.com).

When setting up a subdomain, it’s advisable to use well-established naming conventions, such as ‘mail’ (with other examples available here), rather than experimenting with novel or untested names.

In summary, Gmail’s Postmaster Tools V2 provides valuable insights into how email compliance is evaluated. These updates remind us that the interconnected relationship between subdomains and organizational domains is more than just a technical detail, it’s an important factor in email deliverability.