DMARC and the Rise of Sending Subdomains: A Guide for High-Volume Emailers


I’m trying to understand the necessity of this change. Why isn’t it sufficient anymore to send emails from a service provider’s domain with a ‘reply-to’ address from our own domain?

This inquiry is particularly relevant as I manage a client’s email system that sends around 3,000 to 4,000 emails daily. They currently use a traditional method of sending from ‘[email protected]’ with customer-specific ‘reply-to’ addresses. With Gmail and Yahoo’s stricter policies for bulk senders, I want to ensure that my client’s setup is compliant for future scalability.

In my recent research, I’ve come across information suggesting that DMARC policies may treat emails with ‘reply-to’ addresses as suspicious or spam, especially if they seem to redirect replies to an unauthorized domain. It seems that the shift to using specific sending subdomains with proper DMARC records is to avoid these issues.

Please correct me if I’m wrong or if there’s something I’m missing. I’ve also noted that these stringent requirements might only apply to senders who exceed 5,000 emails to Gmail per day, a threshold my client is not likely to reach soon.”


Email service providers like Gmail and Yahoo have been tightening their security measures to combat spam and phishing. These measures include stricter enforcement of authentication protocols such as SPF, DKIM, and DMARC. The traditional method of sending emails from a service provider’s domain with a ‘reply-to’ address from your own domain is becoming less effective because it can be exploited by attackers to mask their identity.

Why ‘Reply-To’ is No Longer Preferred

The ‘reply-to’ header in emails allows senders to specify a different address for recipients to respond to. However, this can be problematic when it comes to DMARC, which is designed to verify that the sender’s domain in the ‘From’ header is authorized to send emails. If the ‘reply-to’ domain differs from the ‘From’ domain, DMARC may flag the email as potentially fraudulent, especially if the ‘reply-to’ domain does not have proper DMARC records.

The Shift to Sending Subdomains

To comply with DMARC policies and ensure deliverability, it’s becoming a best practice to use specific sending subdomains that align with your domain’s DMARC records. This approach helps maintain the integrity of the ‘From’ domain and reduces the risk of your emails being marked as spam or phishing attempts.

Scalability and Compliance

For businesses that send a significant volume of emails, like your client who sends 3,000 to 4,000 emails daily, it’s crucial to have a setup that is scalable and compliant with the latest security standards. By using a dedicated sending subdomain with proper DNS records, you can improve the reputation of your email sending practices and ensure better deliverability.


While your client may not currently exceed the threshold of 5,000 emails to Gmail per day, preparing for future growth and potential policy changes is wise. Setting up specific sending subdomains with proper DMARC records is a proactive step towards maintaining a robust and secure email system. It’s a strategic move that not only aligns with current best practices but also positions your client favorably for any upcoming shifts in email security protocols.

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