Email Attachments

Updated

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.

 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.

  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.

 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 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.

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