40

Email Attachments

Customer.io doesn’t support attachments of any type in Campaigns or Broadcasts. But, there are other, better ways to send files to recipients!

Why you shouldn’t send attachments

Sending attachments can create problems for your deliverability. Here’s a non-exhaustive list of potential problems stemming from attachments:

• Email attachments are often used to hide viruses and malware, so they are more likely to end up in spam folders or flagged as potentially malicious.
• Some email servers have strict policies around message size limits and/or attachments which can cause messages to bounce.
• Attachments impose a larger download for recipients, which can impact their data consumption and/or lead them to ignore your email.

All of these can damage your deliverability.

Send a link rather than an attachment

If you want to send a file to your recipients, the best approach is to send them a link to a landing page where they can download the file.

1. You should host the file online—either on your own server or a cloud storage service like AWS S3, Google Drive, Dropbox, Box, etc.
2. Create a page that links to the file. Your hosting service might already create one for you. Otherwise, you’ll need to add a page to your website.
3. Copy that page’s URL and use it in your email.

Send attachments with transactional messages

In cases where an attachment is unavoidable, you can send them using our Transactional API through an attachments parameter.

With this parameter, you can specify a dictionary of attachments where the filename is the key and the value is the base64-encoded content. The total size of all attachments must be less than 2 MB. Do note that some filetype extensions are restricted.

Move from the events API to the transactional API

Before we released our Transactional API, you could send an attachment as a part of an event. This workaround for attachments was less performant and more restrictive than the attachment support available with the Transactional API. We deprecated attachment support in the Events API on May 10, 2023. If you want to send attachments in your messages, you’ll need to use the Transactional API.

In events, you could pass custom data and attachments as a part of the data object. In a transactional message, you’ll send custom data as a part of the message_data object, and attachments in their own attachments object.

The examples below show how to send a purchase receipt using transactional messages, and how you would have done so with the deprecated event parameter attachments.

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16

POST https://api.customer.io/v1/send/email

{
  "transactional_message_id": "purchase_confirmation",
  "to": "customer@example.com",
  "identifiers": {
    "id": {identifier}
  },
  "message_data": {
    "price": 23.45,
    "product": "socks"
  },
  "attachments": {
    "receipt.pdf": "base64-encoded pdf"
  }
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13

POST https://track.customer.io/api/v1/customers/{identifier}/events 

{
  "name": "purchase",
  "data": {
    "price": 23.45,
    "product": "socks"
    // deprecated attachments object
    "attachments": {
      "receipt.pdf": "base64-encoded pdf"
    }
  }
}

See the transactional message endpoint for a complete list of available properties.