Introducing SRS (Sender Rewrite Scheme) to Make Email Forwarding More Reliable Than Ever

Email services have always been an integral part of SiteGround’s hosting offerings, and our customers heavily rely on them. Every day, we process hundreds of thousands of emails. Many of them are sent out by forwarders set on our servers by our clients. Ensuring the successful delivery of these forwarded emails can be more challenging than you think, as sender verification is not as straightforward as with direct emails.

With the introduction of our own Spam Protection system, we now have more options to enhance the handling of our outgoing email traffic. It allowed us to become one of the few hosting companies to implement Sender Rewrite Scheme (or Mail SRS) and thus significantly improve email forwarding delivery rates for our clients. Here are the details of how this new functionality works and how it benefits our users.

Why are forwarded emails harder to deliver?

Usually, when there is an incoming email, the receiving server tries to identify if the sending server is legitimate and if the email should be accepted. The purpose of this check is to prevent malicious senders from reaching your inbox (for example, a scam email pretending to be coming from your bank’s domain name). 

Domain names used for legitimate email sending need to have an SPF (Sender Policy Framework) record, that defines the IP addresses or hosts that are allowed (or not allowed) to send messages on behalf of this domain. 

In the Email Forwarding scenario, we have a Sender, who is sending an email to a destination address and after that, the destination address forwards the mail to its end recipient. This means that the end recipient is receiving an email coming from a “mediator” server, which might not be allowed to send messages on behalf of the sending domain, according to its SPF record.

This, based on the receiving servers’s policies, can result in mails being rejected or sent to your Spam folder due to SPF (Sender Policy Framework) failure.

How does SRS make email forwarding more reliable?

Sender Rewrite Scheme (or Mail SRS) is a mechanism that provides a solution in cases of email forwarding so that SPF failures can be avoided. This way legitimate forwarded mails can be successfully accepted from the receiving mail server.

SRS works by rewriting some of the metadata in the email messages after it’s passed the mediator server, “instructing” the destination mail server to check the SPF against the forwarding server, not the original sender’s domain. That way, the SPF check would pass because the forwarding server’s IP would match the sender’s address. Here is a real-life example of how this works:

Imagine a service you use (your bank, for example), sends an email to your business email address webmaster@yourdomain.com, which is hosted with SiteGround. The mail comes from your bank’s IP and its “from” address is billing@yourbank.com, for example – as these two are matching the SPF check passes and the mail is delivered to webmaster@yourdomain.com.

Now imagine that you would like to have this email forwarded from your business email  webmaster@yourdomain.com to your personal email name@gmail.com. 

If there is no SRS, Gmail will see an email sent from billing@yourbank.com but coming from a SiteGround IP.  As these two do not match, the SPF check will not pass and Gmail will probably deliver the mail to the Spam folder. 

If SRS is configured correctly, the “from” address will be changed to webmaster@yourdomain.com to match the SiteGround IP as its host. As these are matching, the SPF check will pass and you will receive the important email from your bank in your personal mailbox as well.

This makes SRS an important part of each mail server configuration for maintaining the efficiency and reliability of email forwarding services, ensuring that important communications are not mistakenly marked as spam or rejected due to SPF checks.

SRS Implementation Results 

We’re already observing a very positive impact on the deliverability of the forwarded mails after SRS was made available on our servers. Our data shows 0% SPF failures for all forwarded email messages going through our servers, proving incredible stability and reliability of our mail service and improving the reputation of our mail system addresses. Needless to say, all of this directly benefits the mail reputation of the domains of clients hosted on our servers as well. 

We believe that the mail Sender Rewrite Scheme is the best way to ensure trustworthy and reliable email services when it comes to email forwarding. Although it’s popular mainly in mail-specific providers and not so much in the majority of hosting companies, we’ve gone the extra mile to add this super useful and efficient mechanism to enhance the email experience of our clients even further.