---
title: Reply to emails from Workers
description: Build smart auto-responders by replying to incoming emails programmatically with Email Workers.
image: https://developers.cloudflare.com/dev-products-preview.png
---

> Documentation Index  
> Fetch the complete documentation index at: https://developers.cloudflare.com/email-routing/llms.txt  
> Use this file to discover all available pages before exploring further.

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# Reply to emails from Workers

You can reply to incoming emails with another new message and implement smart auto-responders programmatically, adding any content and context in the main body of the message. Think of a customer support email automatically generating a ticket and returning the link to the sender, an out-of-office reply with instructions when you are on vacation, or a detailed explanation of why you rejected an email.

Reply to emails is a new method of the [EmailMessage object](https://developers.cloudflare.com/email-routing/email-workers/runtime-api/#emailmessage-definition) in the Runtime API. Here is how it works:

JavaScript

```

import { EmailMessage } from "cloudflare:email";

import { createMimeMessage } from "mimetext";


export default {

  async email(message, env, ctx) {


    const ticket = createTicket(message);


    const msg = createMimeMessage();

    msg.setHeader("In-Reply-To", message.headers.get("Message-ID"));

    msg.setSender({ name: "Thank you for your contact", addr: "<SENDER>@example.com" });

    msg.setRecipient(message.from);

    msg.setSubject("Email Routing Auto-reply");

    msg.addMessage({

      contentType: 'text/plain',

      data: `We got your message, your ticket number is ${ ticket.id }`

    });


    const replyMessage = new EmailMessage(

      "<SENDER>@example.com",

      message.from,

      msg.asRaw()

    );


    await message.reply(replyMessage);

  }

}


```

To mitigate security risks and abuse, replying to incoming emails has a few requirements and limits:

* The incoming email has to have valid [DMARC ↗](https://www.cloudflare.com/learning/dns/dns-records/dns-dmarc-record/).
* The email can only be replied to once in the same `EmailMessage` event.
* The recipient in the reply must match the incoming sender.
* The outgoing sender domain must match the same domain that received the email.
* Every time an email passes through Email Routing or another MTA, an entry is added to the `References` list. We stop accepting replies to emails with more than 100 `References` entries to prevent abuse or accidental loops.

If these and other internal conditions are not met, `reply()` will fail with an exception. Otherwise, you can freely compose your reply message, send it back to the original sender, and receive subsequent replies multiple times.

```json
{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/directory/","name":"Directory"}},{"@type":"ListItem","position":2,"item":{"@id":"/email-routing/","name":"Email Routing"}},{"@type":"ListItem","position":3,"item":{"@id":"/email-routing/email-workers/","name":"Email Workers"}},{"@type":"ListItem","position":4,"item":{"@id":"/email-routing/email-workers/reply-email-workers/","name":"Reply to emails from Workers"}}]}
```