Choose a Submission Method

Before submitting messages to the Digital Post Platform, choose how the message files should be provided to the platform.

The platform supports two submission methods:

S3 Upload Method
Direct Multipart Submission

Both methods use envelope files to describe the messages to be delivered. Each envelope defines the recipient, sender, message title, and references to the message body and any attachments.

The main difference is how the envelope files and referenced content files are transferred to the platform.

Option 1: S3 Upload Method

Use the S3 Upload Method when you want to stage envelope files and message content in an S3-compatible storage service before starting delivery processing.

With this method, you:

Create envelope files
Prepare message body files and attachments
Upload the envelope files and referenced content files to an S3-compatible bucket
Call the delivery API with the S3 bucket connection details
Use the returned delivery ID to monitor delivery status

The platform retrieves the envelope files and message content from the configured S3 bucket during delivery processing.

This method is typically suitable when:

Files are already stored or generated in object storage
You are submitting larger batches of messages
You want to prepare and verify the file structure before creating the delivery
You need additional control over storage, access, or optional file encryption

Use this method if your integration is based on uploading files to S3 first.

Option 2: Direct Multipart Submission

Use Direct Multipart Submission when you want to send all required files directly to the platform in a single HTTP request.

With this method, you:

Create envelope files
Prepare message body files and attachments
Submit the envelope files and referenced content files directly using a multipart/form-data POST request
Use the external transaction ID to monitor delivery status

The platform receives the files in the request, stores them internally, validates the envelopes and content, and starts delivery processing.

This method is typically suitable when:

You do not want to use S3-compatible storage
You want to submit a message bundle directly from your application
You are building a simpler integration where all files are available at request time
You want to avoid managing bucket structure, S3 credentials, and S3 object access

Use this method if your integration should send all files directly to the platform.

Comparison

Requirement	S3 Upload Method	Direct Multipart Submission
File transfer method	Files are uploaded to an S3-compatible bucket before delivery is created	Files are included directly in a multipart POST request
Storage responsibility	Sender provides and manages the storage location	Platform handles storage internally after upload
Delivery request	JSON request with S3 connection details	`multipart/form-data` request containing envelopes and content files
File references	Envelope file references must match files uploaded under the expected S3 prefixes	Envelope file references must match multipart section names and filenames
Tracking identifier	Delivery ID returned by the delivery API	External transaction ID provided by the sender
Optional file encryption	Relevant for files uploaded to S3	Not applicable to the S3 file encryption flow

Which method should I choose?

Choose S3 Upload Method if your integration prepares files in object storage before submitting them for delivery.

Choose Direct Multipart Submission if your integration should submit all envelope files, message body files, and attachments directly to the platform without using S3.

Next steps

After choosing a submission method, continue with the relevant guide:

S3 Upload Method — Upload Content to S3 for uploading files to S3-compatible storage and creating a delivery from the uploaded files
Direct Multipart Submission — Send Messages via Multipart for submitting envelope files and content directly using a multipart POST request
Verify and Troubleshoot