Sender Rewriting Scheme (SRS): Your essential guide to secure email forwarding
The Sender Rewriting Scheme (SRS) ensures forwarded emails pass authentication without being blocked or marked as spam. By rewriting the sender address, SRS protects deliverability, preserves sender reputation, and keeps communication seamless across complex infrastructures.
Book a demo to learn more about enhancing your email deliverability.
What is SRS?
SRS is a technique designed to fix one of email’s biggest challenges: Sender Policy Framework (SPF) failures during forwarding. Without it, forwarded emails often fail SPF checks and get rejected or land in spam.
SRS works by rewriting the “envelope sender” to show the forwarding server’s domain while securely encoding the original sender’s details.
This ensures:
- Forwarded emails pass SPF authentication
- Delivery remains reliable, even across complex infrastructures
- The original sender’s identity stays traceable for troubleshooting and replies
With SRS in place, organizations protect sender reputation, reduce false rejections, and maintain a seamless user experience.
Why is SRS important for email authentication?
SRS is essential for reliable email forwarding. Without it, forwarding often triggers SPF failures – leading to blocked messages, lost sales, and inefficient workflows.
By enabling SRS, businesses gain:
- SPF-authenticated forwarding – Forwarded email passes checks, improving deliverability and trust
- Domain reputation protection – Prevents the sender domains from being blacklisted by the SPF records
- Reliable bounce management – Ensures failed deliveries return to the correct sender
Many companies underestimate how much forwarding happens within their environments. From external partners forwarding reports to customer queries, every forwarded message is a potential SPF failure without SRS.
This can have knock-on effects such as clients not receiving important order confirmations, internal teams missing alerts, or executives losing visibility of critical communications. By using the technique, organizations maintain both operational continuity and customer confidence.
How does SRS work?
SRS solves forwarding problems by rewriting the “envelope sender” so that forwarded emails pass SPF checks.
Here is how it works:
- The forwarding server intercepts the outgoing email.
- It rewrites the original ‘Return-Path’ into an address, encoding the sender and a secret key.
- If a bounce occurs, the system decodes the address and returns it to the original sender.
Think of SRS as a “translator” for email authentication. The forwarding server speaks on behalf of the original sender but adds just enough encoded information to make sure the real sender is never lost in the process.
This makes troubleshooting easier because administrators can always trace a bounced or failed message back to its source. For businesses dealing with high email volumes, traceability isn’t only helpful – it’s essential for reliable operations.
Common use cases for SRS
SRS is vital whenever email forwarding is part of workflows. Real-world examples include:
- Mailing lists – Ensures replies and bounces route correctly when messages are forwarded on behalf of members.
- Company process automation – Keeps ticketing systems, notifications, and workflow rules functioning reliably.
- Internal communications – Maintains authentication when messages move between subdomains, departments, or hybrid-cloud systems.
Today, SRS is a reliable solution for any organization committed to high deliverability and trusted forwarding.
A practical example:
Imagine an employee forwards all incoming mail from their corporate address to a colleague’s personal mailbox for convenience. Without SRS, those messages could silently fail SPF checks, causing them to never arrive. The colleague might believe no one is emailing them when, in reality, messages are being blocked.
SRS and email security protocols
Email security relies on multiple protocols and techniques working together. SRS plays a key role by strengthening forwarding while complementing email authentication standards:
- SPF – SRS fixes SPF’s blind spot by rewriting the ‘Return-Path’ so forwarded messages don’t fail authentication.
- DomainKeys Identified Mail (DKIM) – To avoid DKIM failures, the forwarding server can either re-sign the message with its own DKIM key or use a relaxed algorithm that ignores the changes in the header.
- Domain-based Message Authentication, Reporting, and Conformance (DMARC) – SRS and DMARC work together to improve email authentication and deliverability, especially for messages that are forwarded by third-party servers.
A layered approach using SRS, SPF, DKIM, and DMARC ensures secure, compliant, and reliable email delivery across today’s complex infrastructures.
Book a demo today to see how Sendmarc’s DMARC solution simplifies the implementation of these protocols to protect your domains, preserve deliverability, and strengthen trust in every message.
Troubleshooting and common SRS issues
Even with SRS in place, forwarding setups can run into challenges.
Common issues include:
- DMARC misalignment – Forwarded emails can still fail DMARC if neither SPF nor DKIM aligns. Ongoing monitoring helps reduce risk.
- Address length and chaining – Multiple forwards can create long, complex SRS addresses that may hit system limits.
- Spoofing vulnerability – SRS addresses can be spoofed or forged if the secret key is compromised.
Tip: Test forwarding with SRS enabled before rolling out migrations or bulk changes.
With the right configuration and monitoring, SRS remains a reliable solution for forwarding.
Book a demo to secure your email
SRS plays an important role in making email forwarding work with modern authentication, but true protection requires a full security framework. With DMARC in place, your business ensures SPF and DKIM are enforced and every message is verified end-to-end.
Book a demo today to see how Sendmarc’s DMARC solution safeguards your domains, preserves deliverability, and strengthens trust in every email.
SRS FAQs
What is SRS?
Sender Rewriting Scheme (SRS) is a technique that rewrites the “envelope sender” address on forwarded emails to prevent Sender Policy Framework (SPF) failures. SRS ensures forwarded messages are delivered reliably.
What is the main purpose of SRS?
The main purpose of SRS is to allow forwarded emails to continue passing SPF checks. By doing this, SRS prevents DNS-based rejections and keeps legitimate communications flowing without disruption.
How does SRS interact with DMARC and DKIM?
SRS supports Sender Policy Framework (SPF) continuity during forwarding. For Domain-based Message Authentication, Reporting, and Conformance (DMARC), messages pass only if SPF and/or DomainKeys Identified Mail (DKIM) align. SRS improves SPF pass rates but doesn’t guarantee DMARC alignment in every forwarding scenario.
Who benefits from SRS?
SRS benefits companies and individuals who rely on email forwarding. This helps them avoid authentication errors and improve deliverability.
Does SRS affect end users or the way emails appear?
No, Sender Rewriting Scheme (SRS) doesn’t affect end users or email appearance. It operates entirely behind the scenes at the server level. End users won’t notice any difference in the way emails appear in their inboxes or how they interact with them.
The only change occurs in the “envelope sender” field, which is invisible to most users. This means organizations can strengthen authentication and protect deliverability without altering the user experience.