> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sendkit.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Return-Path

> Learn what the Return-Path is and how it relates to bounces and SPF authentication.

## What is the Return-Path?

The Return-Path (also called the envelope sender, bounce address, or MAIL FROM) is the email address where bounce notifications are sent when an email can't be delivered. It's a hidden header — recipients don't see it, but mail servers use it for routing bounce messages.

It's separate from the `From` header that recipients see in their inbox.

## Return-Path vs From

| Header          | Who sees it       | Purpose                          | Example                 |
| --------------- | ----------------- | -------------------------------- | ----------------------- |
| **From**        | The recipient     | Displays the sender in the inbox | `hello@acme.com`        |
| **Return-Path** | Mail servers only | Receives bounce notifications    | `bounces@send.acme.com` |

These are often different addresses. When you send through SendKit, the `From` address is your sender (e.g., `hello@acme.com`), but the Return-Path is set to a SendKit address on the `send` subdomain so we can process bounces for you.

## How it works

<Steps>
  <Step title="You send an email">
    The email has `From: hello@acme.com` and `Return-Path: bounces@send.acme.com`.
  </Step>

  <Step title="Recipient's mail server receives it">
    If delivery succeeds, the process is complete.
  </Step>

  <Step title="If delivery fails (bounce)">
    The bounce notification is sent to the Return-Path address: `bounces@send.acme.com`.
  </Step>

  <Step title="SendKit processes the bounce">
    The email is marked as bounced, the `email.bounced` webhook fires, and the address is added to the suppression list (if hard bounce).
  </Step>
</Steps>

## Return-Path and SPF

SPF authentication checks the **Return-Path domain**, not the `From` domain. This is an important distinction.

When SendKit sends an email from `hello@acme.com` with a Return-Path of `bounces@send.acme.com`, the receiving server checks the SPF record of `send.acme.com` — not `acme.com`.

This is why SendKit asks you to add the SPF record on the `send` subdomain:

| Header checked                       | Domain checked  | DNS record location               |
| ------------------------------------ | --------------- | --------------------------------- |
| Return-Path: `bounces@send.acme.com` | `send.acme.com` | SPF TXT record on `send.acme.com` |

And why DMARC's **alignment** check matters — it verifies that the Return-Path domain and the `From` domain are related. Since `send.acme.com` is a subdomain of `acme.com`, relaxed alignment passes.

## Custom Return-Path

By default, SendKit uses the `send` subdomain for the Return-Path (e.g., `bounces@send.acme.com`). This is automatically configured when you verify your domain.

The `send` subdomain was chosen because:

* It clearly identifies the purpose (sending email)
* It keeps bounce handling separate from your main email
* It doesn't interfere with your root domain's email configuration

## Why the Return-Path matters

### 1. Bounce processing

Without a proper Return-Path, bounce notifications have nowhere to go. You'd lose visibility into delivery failures, and your list would accumulate invalid addresses — destroying your reputation over time.

### 2. SPF alignment

SPF checks the Return-Path domain. If the Return-Path domain doesn't have an SPF record or it doesn't include the sending server, SPF fails.

### 3. DMARC alignment

DMARC checks that the Return-Path domain (SPF) or DKIM domain aligns with the `From` domain. For SPF alignment, the Return-Path domain must match or be a subdomain of the `From` domain.

## FAQ

<AccordionGroup>
  <Accordion title="Can I customize the Return-Path?">
    The Return-Path subdomain is `send` by default when you verify a domain in SendKit. This is configured automatically when you add the required DNS records.
  </Accordion>

  <Accordion title="Why doesn't the Return-Path match the From address?">
    This is normal and expected when using an email service like SendKit. The Return-Path is set to a SendKit-managed address so that bounce notifications are routed to SendKit for processing. DMARC alignment ensures the two domains are related (via subdomain matching).
  </Accordion>

  <Accordion title="Does the recipient see the Return-Path?">
    No. The Return-Path is part of the email's hidden headers. Recipients only see the `From` address. Some email clients let you view full headers (which includes the Return-Path), but this is not shown by default.
  </Accordion>
</AccordionGroup>