Customer.io doesn’t support attachments of any type in Campaigns or Broadcasts. But, there are other, better ways to send files to recipients!
Try sending a transactional message
Rather than trying to send links, or add attachments to events, you can send attachments as a part of our transactional message service.
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
Include PDF attachments from the asset library
While you can encode attachment and send them directly to people, you can also host PDFs in our asset library and link to them in your messages. This can save you the trouble of encoding and sending files directly.
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.
- You should host the file online—either on your own server or a cloud storage service like AWS S3, Google Drive, Dropbox, Box, etc.
- 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.
- Copy that page’s URL and use it in your email.
Avoid sending a link to a file directly
You can send a link to the file itself, but be aware that some spam filters and algorithms have been known to follow links to evaluate them, and if the link leads to a file, it could be considered suspicious. Microsoft Office files are particularly risky.
While more convoluted than using a direct link, this approach helps ensure that your emails are not flagged as spam.
Send attachments with transactional messages
In cases where an attachment is unavoidable, you can send them using our Transactional API through an
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
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
|Transactional message with attachments||Purchase event with deprecated attachments key|
See the transactional message endpoint for a complete list of available properties.