What Is Return-Path Header (And Why It Matters)

May 15, 2023
Written by
Jesse Sumrak
Opinions expressed by Twilio contributors are their own

What Is Return-Path Header (And Why It Matters)

We can all agree that email communication is essential for successful businesses. However, for your emails to be successful and produce conversions, they have to land in the inbox. 

But what happens when emails don’t make it to the inbox? Where do they go when they bounce? How are they processed?
Enter return-path email headers.

What is return path email header?

Return-path is a hidden email header that indicates where and how bounced emails will be processed. This header, also referred to as a bounce address or reverse path, is an SMTP address that is separate from your original sending address, and is used specifically for collecting and processing bounced messages.

Having a clear return-path system in place is incredibly important for your email program. It acts as a safeguard, protecting senders by providing a separate location for processing bounced emails. Your original sending inbox isn’t crowded by those “failed delivery” emails and that bounced messages are kept organized and together. Having a clear, organized return-path for bounced messages can also help your email deliverability and maintain your sending reputation.

Why is return-path important?

Return-path is an important tool to have at your disposal, especially for mass email sends. Let’s say you’re sending an email blast about an offer your company is promoting to your entire email list. While we don’t want to see bounced emails, the reality is that messages can and do bounce for a variety of reasons. 

When you’re sending to large groups, you can get tens, maybe even hundreds of bounced messages depending on the size and nature of your campaign. These “failed delivery” messages then come back to haunt and crowd your original sending inbox. Instead, by having an established return-path, those messages are processed and stored separately in their own specified inbox.

Return-path also helps with your deliverability and sending reputation by helping to validate your identity as a sender (i.e. whether or not you’re sending spam). Because return-path is a SMTP address, it can be used by servers and inbox providers to decide how or if they want to filter your messages. Having a properly set-up return-path can help provide credibility for your messages and subsequently you, the sender, which in turn boosts your sending reputation.

How return-path works

Return-path works by directing where bounced messages should go when they cannot be delivered. It is usually set up by a developer or email platform provider but can be customized using the Domain Authentication doc in our Knowledge Center

When a server or inbox provider receives your message, they validate your identity as a sender as well as your sending reputation before pushing you through to your intended recipients’ inboxes. 

In this validation process, DMARC and return-path work together to get you through these filters. DMARC examines your message to confirm that the domain provided in the “sent from” field matches the domain provided in the return-path field, which helps to validate your identity as a sender. Once these domains have been confirmed and matched by DMARC, you’ll have an easier time getting through filters set by servers and inbox providers.

Types of bounced emails

There are two types of bounced emails: hard bounces and soft bounces.

Hard bounces occur when there are permanent issues with a recipient, including an invalid email address or typo in your mailing list.

Soft bounces are more temporary and usually occur when there’s a problem with a recipient’s inbox, including file size or attachments issues or the possibility of a recipient having a full inbox. 

When a message hard bounces, the general best practice is to check that there are no typos in the recipient’s address. If there are none, you should remove the address from your mailing list. Keeping email addresses that hard bounce can damage your reputation as a sender and affect your deliverability in the long run. 

When an email soft bounces, you have a little bit more wiggle room than with a hard bounce. Email addresses that soft bounce can be kept in your mailing list for future campaigns, but you’ll want to watch them to see if they bounce again. If they continue to bounce, they should be removed from your mailing list.

How to customize your return-path in SendGrid

Twilio SendGrid sets up an automatic return-path for our customers. This helps us protect both you and your customers, as well as give your deliverability a boost! However, your return-path can be customized during the domain authentication process.

When you are in the process of authenticating a domain, open the advanced settings found on the same screen used to input the domain settings. From there, you’ll be able to build a custom return-path. However, for this process to work, you must use different characters from the ones that Twilio SendGrid automatically assigned to you. 

Having a clear, systematic return-path is essential to creating a successful email program and improving your deliverability. For best practice tips on improving deliverability and developing strong email communication strategies, check out our blog.

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