inline_attachment_demo

Inline Attachment Example

This example demonstrates how to send messages and drafts with inline attachments using the content_id field in the Nylas Python SDK.

What This Example Shows

• How to create inline attachments with content_id for HTML emails
• How the SDK properly handles content_id for large attachments (>3MB)
• The difference between inline attachments and regular attachments
• How to reference inline attachments in HTML email bodies using cid: syntax

Key Features Demonstrated

Content ID Usage

When an attachment includes a content_id field, the SDK will use this as the field name in multipart form data instead of the generic file{index} pattern. This is crucial for inline attachments that need to be referenced in the email body.

HTML Email with Inline Images

The example shows how to:

1. Set the content_id field in the attachment
2. Reference the attachment in HTML using src="cid:your-content-id"
3. Set appropriate inline properties (is_inline: True, content_disposition: "inline")

Large Attachment Handling

For attachments larger than 3MB, the SDK automatically switches from JSON to multipart form data. With this fix, the content_id is now properly respected in the form field names.

Running the Example

1. Set your Nylas API key:

   export NYLAS_API_KEY='your-api-key-here'

2. Update the grant ID and email addresses in the script

3. Run the example:

   python inline_attachment_example.py

Important Notes

• Content ID Format: Use a unique identifier for each inline attachment (e.g., "image1@example.com", "logo", "banner-image")
• HTML Reference: Reference inline attachments in HTML using src="cid:your-content-id"
• Backward Compatibility: Attachments without content_id still work as before using file{index} naming
• File Size Threshold: The 3MB threshold determines whether JSON or form data is used for the request

Expected Behavior

Before the Fix (Problematic)

Form data fields:
- message: (JSON payload)
- file0: (inline image - content_id ignored)
- file1: (regular attachment)

After the Fix (Correct)

Form data fields:
- message: (JSON payload)
- my-inline-image: (inline image - uses content_id)
- file1: (regular attachment - fallback to file{index})

This ensures that email clients can properly display inline images by matching the content_id in the HTML cid: reference with the multipart form field name.