Email attachments

1. Set an attachment key in your email template to tell Knock how to resolve attachments you send in the data payload of your trigger call. To set an attachment key, click the gear icon (⚙️) at the top of the email template editor, then set your desired key under the "Attachment key" field. This key will default to attachments if not specified.
2. Include one or more attachment objects in the data payload of your trigger call, under the configured attachment key. Each attachment object should have the content of the file to be attached as a base64 encoded value.
3. Knock automatically adds any attachments included in the attachment key of your trigger call to the emails sent by your email provider 🎉.

Every attachment you send to Knock in your data payload should include the following properties (those marked with an * are required):

Property	Description
name*	The name of the file
content_type*	A mime type for the file
content*	The base64 encoded file content (up to 10mb)
content_id	An optional unique Content-ID for the attachment, which will automatically set the attachment as inline. Currently only supported for SendGrid and Postmark. See Referencing attachment files inline for more details.

Note: each attachment object must be less than 10mb, but you should confirm whether your email provider has a lower limit.

Once you've specified your attachment key in your email template, the last step is to send the data along to Knock. Remember that you need to base64 encode the contents of the file.

Note: you can send multiple attachments for an email by including an array of attachment objects under the attachment key in your data payload.

If you need to send a different attachment per recipient in a workflow then you'll need to make one trigger call per recipient, such that the data payload is unique to that recipient.

If you're using SendGrid or Postmark as your email provider, you can reference attachment files inline in your email template by providing a content_id property on the attachment object you send in your trigger call. Adding a content_id to the attachment embeds it in the email as an inline attachment, which you can reference in your template using the cid: prefix and the content_id value.

The Knock dashboard does not currently support previewing the attachment files that are sent with your email messages. This means that you'll need to send a test message (via the workflow test runner or the API) to your own email inbox to see what the attachment(s) will look like.

This limitation applies to both regular attachment files and inline attachments. Any images that are sent as inline attachments will not be viewable in the dashboard.