How do I ensure email deliverability with different return-path addresses and subdomains?
Matthew Whittaker
Co-founder & CTO, Suped
Published 5 Jun 2025
Updated 16 Aug 2025
7 min read
Navigating the complexities of email deliverability often involves understanding how different technical elements interact. Two crucial components that frequently come up are return-path addresses and subdomains. Properly configuring these can significantly impact whether your emails land in the inbox or get lost along the way.
I've seen many senders grapple with ensuring their legitimate emails reach recipients, especially when trying to maintain separate sending reputations for different types of mail. The good news is that with careful planning and adherence to best practices, you can successfully manage email deliverability even with varied return-path addresses and subdomains.
The role of return-path in email delivery
The return-path address, also known as the Mail From address or Bounce address, is specified in the email header and tells receiving mail servers where to send bounce messages and other delivery notifications. It's a critical component for processing undeliverable emails and maintaining a clean sender list. Without a valid return-path, bounces can go unnoticed, leading to issues like sending to invalid addresses and a degraded sender reputation.
Using a custom return-path (meaning one that matches your sending domain or a related subdomain) can boost your branding and provide better insights into your email stream. For instance, if your 'From' address is newsletter@yourdomain.com, a custom return-path like bounces@return.yourdomain.com aligns your brand throughout the email lifecycle. This practice helps ensure successful delivery and bounce handling according to Abnormal Security.
Crucially, both the 'From' address and the return-path domain must be configured to accept mail. If a receiving server attempts to send a bounce notification to a non-existent return-path address, it can lead to further deliverability problems or even cause your sending IP to be added to a blocklist (or blacklist). Ensure that any domain you use in your return-path has a valid MX record pointing to a mail server that can handle incoming mail, even if it's just to capture bounces.
Example of a Return-Path CNAME RecordDNS
yourdomain.com. IN CNAME bounces.sendgrid.net.
A common configuration involves setting up a CNAME record for your return-path to point to your email service provider's bounce handling domain. This allows the ESP to manage bounces on your behalf, while still associating the return-path with your domain, contributing to better email deliverability and sender reputation.
Leveraging subdomains for reputation management
Subdomains are essentially segmented parts of your main domain, such as marketing.yourdomain.com or transactional.yourdomain.com. Their primary advantage in email sending is the ability to separate sender reputation for different types of email traffic. This means if your marketing emails encounter deliverability issues, they won't necessarily impact the deliverability of your critical transactional emails, and vice versa.
Consider using separate subdomains for distinct email categories. For instance, newsletter.yourdomain.com for bulk marketing emails and receipts.yourdomain.com for order confirmations. This segregation protects your main domain's reputation and helps ensure that essential messages always get through. This is a common strategy for email deliverability for businesses according to Courier.
When deciding whether to use subdomains for outbound email delivery, consider the volume and nature of your email sends. High-volume marketing campaigns carry more risk than low-volume transactional messages. Using a dedicated subdomain allows you to warm up its sending reputation independently and insulate your primary domain from potential blocklists or (blacklists).
Root domain sending
Reputation risk: All email types share a single reputation, making it vulnerable to issues from any send type.
Bounce handling: Bounces for all email streams are typically handled by the same system.
Simplicity: Easier to set up initially, but harder to manage reputation long-term.
Subdomain sending
Reputation isolation: Each subdomain has its own reputation, protecting your main domain and other streams.
Granular bounce handling: Allows for specific return-paths per subdomain, improving analytics.
Scalability: Better for large-volume senders or those with diverse email types.
Authentication and alignment with varied addresses
Regardless of whether you use different return-path addresses or subdomains, proper email authentication is non-negotiable. This includes Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM), and Domain-based Message Authentication, Reporting, and Conformance (DMARC).
SPF alignment dictates that the domain in the Return-Path (Mail From) header must match the domain in the 'From' address (visible to recipients) or a designated authorized sending domain. DKIM alignment ensures that the domain signing the email (the d= tag in the DKIM signature) aligns with the 'From' domain. While DKIM often uses a subdomain for signing, it must align with your primary 'From' domain to pass authentication checks effectively.
DMARC builds upon SPF and DKIM by adding a policy layer and reporting capabilities. For DMARC to pass, either the SPF-aligned domain (Return-Path domain) or the DKIM-aligned domain must match the 'From' domain. This identifier alignment is crucial for preventing spoofing and improving deliverability, as detailed in MailerLite's guide to domain alignment. Setting up these records correctly for each subdomain and return-path is essential.
DMARC alignment best practices
I always recommend configuring DMARC for all your sending domains and subdomains. It provides valuable insights into your email ecosystem and allows you to enforce policies against unauthorized use of your domain.
Start with a relaxed policy (p=none): This allows you to monitor DMARC reports without impacting legitimate email delivery.
Analyze DMARC reports: Identify legitimate sending sources that might not be aligning correctly.
Progress gradually: Move to quarantine (p=quarantine) and then reject (p=reject) as confidence grows.
Beyond technical configurations, maintaining a positive sender reputation is paramount. This involves consistent list hygiene, promptly removing invalid or unengaged addresses, and avoiding spam traps. Regularly monitoring your bounce rates and checking blocklists (or blacklists) is crucial, even for subdomains.
When introducing new subdomains or significantly changing your sending patterns, implement a thorough warmup process. This gradually builds trust with Internet Service Providers (ISPs) by slowly increasing your sending volume. Rushing this can trigger spam filters and lead to poor deliverability. A dedicated IP address may also be considered for high-volume senders, giving them full control over their reputation.
Continuously test your email deliverability. Use an email deliverability tester to see how your emails perform across different mailbox providers. This proactive approach helps identify and address potential issues before they impact your campaigns. Maintaining a high level of engagement with your recipients, reducing complaints, and ensuring your content is relevant are also vital for long-term success.
Regularly clean your lists: Remove inactive subscribers and hard bounces to prevent deliverability issues.
Segment email types: Use subdomains to isolate the reputation of marketing and transactional emails.
Ensure return-path validity: Always configure MX records for your return-path domains to receive bounces.
Monitor blocklists: Keep an eye on your sending domains and IPs to detect any listing issues promptly.
Implement DMARC: This is fundamental for authentication and gaining visibility into your email traffic.
Views from the trenches
Best practices
Always ensure that the 'From' address domain and the Return-Path domain have valid MX records and are capable of receiving email, even if it's just for bounce processing.
Utilize subdomains to segment your email sending traffic, separating marketing campaigns from transactional messages to protect your main domain's reputation.
Implement strong email authentication (SPF, DKIM, DMARC) for all your sending domains and subdomains to ensure proper alignment and prevent spoofing.
Gradually warm up any new sending subdomains or IP addresses to build a positive sender reputation with Internet Service Providers (ISPs) over time.
Regularly monitor your email deliverability metrics, including bounce rates, complaint rates, and inbox placement across major mailbox providers.
Common pitfalls
Sending email from a 'From' address that cannot receive replies or bounces, which can lead to deliverability problems and a poor sender reputation.
Failing to configure proper MX records for subdomains used in the Return-Path, causing bounce messages to be lost and negatively affecting sender hygiene.
Not aligning SPF or DKIM domains with the 'From' address domain, resulting in DMARC authentication failures and increased chances of emails landing in spam folders.
Ignoring DMARC reports, missing critical insights into unauthorized sending or misconfigurations that impact email deliverability.
Suddenly increasing email volume on a new subdomain without a proper warmup, which can trigger spam filters and lead to immediate blocklisting (or blacklisting).
Expert tips
For optimal DMARC alignment, aim for both SPF and DKIM domains to match your 'From' domain. This provides the strongest authentication signals.
When using different subdomains, ensure each has its own unique set of DNS records (SPF, DKIM, DMARC, MX) that are correctly configured.
Consider setting up a generic catch-all mailbox for your return-path domains if you don't need to process individual bounces, but still want to accept mail.
Periodically review your sending infrastructure and DNS records to ensure they are up-to-date and compliant with evolving email authentication standards.
Use email feedback loops (FBLs) to receive reports from ISPs about user complaints, which can help you identify and address issues promptly.
Expert view
Expert from Email Geeks says that you should never send mail with a 'From' address that cannot receive mail, as this will lead to deliverability problems.
2021-09-24 - Email Geeks
Expert view
Expert from Email Geeks says that both the 'From' domain and the return-path domain should be configured to accept mail, ensuring bounces and replies are handled properly.
2021-09-24 - Email Geeks
Key takeaways for reliable email delivery
Effectively managing email deliverability with different return-path addresses and subdomains requires a strategic approach. It's not just about sending emails, but about ensuring they are properly authenticated, routed, and monitored.
By understanding the role of each component, leveraging subdomains for reputation isolation, and diligently implementing authentication protocols, you can significantly improve your chances of reaching the inbox. Continuous monitoring and adaptation to deliverability trends are also key to long-term success.
