Customer.io doesn’t support attachments of any type in Campaigns or Broadcasts. But, there are other, better ways to send files to recipients!
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.
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.
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.
- 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.
Our Transactional API does support attachments through an
You can specify for this parameter a dictionary of attachments where the filename is the key and the value is the base64-encoded contents. The total size of all attachments must be less than 2 MB. Do note that some filetype extensions are restricted.