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[CUST-4448] Fix: content id not being respected for large inline attachments. (#440)
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‎CHANGELOG.md‎

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@@ -4,6 +4,7 @@ nylas-python Changelog
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Unreleased
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----------
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* Fixed from field handling in messages.send() to properly map "from_" field to "from field
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* Fixed content_id handling for large inline attachments to use content_id as field name instead of generic file{index}
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v6.12.0
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----------

‎examples/inline_attachment_demo/README.md‎

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# Inline Attachment Example
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This example demonstrates how to send messages and drafts with inline attachments using the `content_id` field in the Nylas Python SDK.
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## What This Example Shows
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- How to create inline attachments with `content_id` for HTML emails
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- How the SDK properly handles `content_id` for large attachments (>3MB)
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- The difference between inline attachments and regular attachments
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- How to reference inline attachments in HTML email bodies using `cid:` syntax
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## Key Features Demonstrated
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### Content ID Usage
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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.
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### HTML Email with Inline Images
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The example shows how to:
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1. Set the `content_id` field in the attachment
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2. Reference the attachment in HTML using `src="cid:your-content-id"`
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3. Set appropriate inline properties (`is_inline: True`, `content_disposition: "inline"`)
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### Large Attachment Handling
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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.
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## Running the Example
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1. Set your Nylas API key:
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```bash
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export NYLAS_API_KEY='your-api-key-here'
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```
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2. Update the grant ID and email addresses in the script
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3. Run the example:
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```bash
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python inline_attachment_example.py
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```
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## Important Notes
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- **Content ID Format**: Use a unique identifier for each inline attachment (e.g., `"[email protected]"`, `"logo"`, `"banner-image"`)
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- **HTML Reference**: Reference inline attachments in HTML using `src="cid:your-content-id"`
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- **Backward Compatibility**: Attachments without `content_id` still work as before using `file{index}` naming
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- **File Size Threshold**: The 3MB threshold determines whether JSON or form data is used for the request
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## Expected Behavior
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### Before the Fix (Problematic)
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```
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Form data fields:
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- message: (JSON payload)
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- file0: (inline image - content_id ignored)
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- file1: (regular attachment)
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```
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### After the Fix (Correct)
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```
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Form data fields:
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- message: (JSON payload)
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- my-inline-image: (inline image - uses content_id)
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- file1: (regular attachment - fallback to file{index})
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```
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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.

‎examples/inline_attachment_demo/inline_attachment_example.py‎

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#!/usr/bin/env python3
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import base64
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import io
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import os
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from nylas import Client
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def send_message_with_inline_attachment():
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"""
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This example demonstrates how to send a message with an inline attachment
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that uses a content_id for referencing in HTML email bodies.
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This is particularly useful for embedding images directly in HTML emails
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where the image is referenced using 'cid:' in the src attribute.
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"""
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# Initialize the Nylas client
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nylas = Client(
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api_key=os.environ.get("NYLAS_API_KEY"), # Replace with your API key
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)
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# Get test email
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test_email = os.environ.get("TEST_EMAIL")
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# Get grant
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grant_id = os.environ.get("NYLAS_GRANT_ID")
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# Create a sample image content using base64 decoded data
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# This is a small PNG image that can be used for demonstration
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base64_image = "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"
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image_content = base64.b64decode(base64_image)
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# Create the message with inline attachment
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message_request = {
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"to": [{"email": test_email, "name": "Recipient Name"}],
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"from": [{"email": test_email, "name": "Sender Name"}],
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"subject": "Message with Inline Image",
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"body": """
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<html>
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<body>
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<h1>Hello!</h1>
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<p>This email contains an inline image:</p>
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<img src="cid:my-inline-image" alt="Inline Image" style="max-width: 200px;">
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<p>The image above is embedded directly in the email using content_id.</p>
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</body>
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</html>
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""",
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"attachments": [
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{
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"filename": "inline-image.png",
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"content_type": "image/png",
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"content": io.BytesIO(image_content),
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"size": len(image_content),
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"content_id": "my-inline-image", # This is the key for inline attachments
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"is_inline": True,
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"content_disposition": "inline"
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},
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{
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# Regular attachment without content_id for comparison
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"filename": "regular-attachment.txt",
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"content_type": "text/plain",
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"content": io.BytesIO(b"This is a regular attachment"),
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"size": 28,
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# No content_id - this will use the default file{index} naming
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}
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]
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}
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try:
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# Send the message
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response = nylas.messages.send(
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identifier=grant_id, # Replace with your grant ID
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request_body=message_request
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)
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print("Message sent successfully!")
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print(f"Message ID: {response.data.id}")
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print(f"Thread ID: {response.data.thread_id}")
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# The inline attachment will be referenced by its content_id in the form data
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# instead of a generic file{index} name, allowing proper inline display
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except Exception as e:
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print(f"Error sending message: {e}")
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def send_draft_with_inline_attachment():
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"""
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This example demonstrates how to create and send a draft with an inline attachment.
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"""
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# Initialize the Nylas client
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nylas = Client(
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api_key=os.environ.get("NYLAS_API_KEY"), # Replace with your API key
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)
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# Get test email
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test_email = os.environ.get("TEST_EMAIL")
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# Get grant
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grant_id = os.environ.get("NYLAS_GRANT_ID")
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# Create a larger image content to trigger form data usage (>3MB threshold)
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# For demo purposes, we'll replicate the same image data multiple times
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# In real usage, large images would automatically use the content_id functionality
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base64_image = "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"
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large_image_content = base64.b64decode(base64_image) * 1000 # Replicated to make it large
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# Create the draft with inline attachment
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draft_request = {
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"to": [{"email": test_email, "name": "Recipient Name"}],
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"from": [{"email": test_email, "name": "Sender Name"}],
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"subject": "Draft with Inline Image",
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"body": """
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<html>
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<body>
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<h1>Draft Email</h1>
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<p>This draft contains an inline image:</p>
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<img src="cid:logo-image" alt="Company Logo" style="max-width: 300px;">
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<p>Best regards,<br>Your Team</p>
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</body>
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</html>
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""",
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"attachments": [
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{
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"filename": "company-logo.png",
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"content_type": "image/png",
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"content": io.BytesIO(large_image_content),
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"size": len(large_image_content),
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"content_id": "logo-image", # Content ID for inline reference
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"is_inline": True,
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"content_disposition": "inline"
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}
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]
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}
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try:
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# Create the draft
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draft_response = nylas.drafts.create(
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identifier=grant_id, # Replace with your grant ID
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request_body=draft_request
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)
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print("Draft created successfully!")
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print(f"Draft ID: {draft_response.data.id}")
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# Send the draft
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send_response = nylas.drafts.send(
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identifier=grant_id, # Replace with your grant ID
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draft_id=draft_response.data.id
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)
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print("Draft sent successfully!")
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print(f"Message ID: {send_response.data.id}")
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except Exception as e:
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print(f"Error with draft: {e}")
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if __name__ == "__main__":
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print("Inline Attachment Example")
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print("=" * 50)
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print()
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# Check if API key is set
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if not os.environ.get("NYLAS_API_KEY"):
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print("Please set the NYLAS_API_KEY environment variable")
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print("export NYLAS_API_KEY='your-api-key-here'")
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exit(1)
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# Check if grant ID is set
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if not os.environ.get("NYLAS_GRANT_ID"):
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print("Please set the NYLAS_GRANT_ID environment variable")
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print("export NYLAS_GRANT_ID='your-grant-id-here'")
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exit(1)
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# Check if test email is set
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if not os.environ.get("TEST_EMAIL"):
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print("Please set the TEST_EMAIL environment variable")
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print("export TEST_EMAIL='your-test-email-here'")
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exit(1)
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print("1. Sending message with inline attachment...")
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send_message_with_inline_attachment()
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print("\n2. Creating and sending draft with inline attachment...")
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send_draft_with_inline_attachment()
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print("\nNote: The content_id field ensures that large inline attachments")
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print("are properly referenced in the multipart form data, allowing")
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print("email clients to display them inline correctly.")

‎nylas/utils/file_utils.py‎

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# Create the multipart/form-data encoder
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fields = {"message": ("", message_payload, "application/json")}
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for index, attachment in enumerate(attachments):
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fields[f"file{index}"] = (
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# Use content_id as field name if provided, otherwise fallback to file{index}
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field_name = attachment.get("content_id", f"file{index}")
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fields[field_name] = (
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attachment["filename"],
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attachment["content"],
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attachment["content_type"],

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