Troubleshooting Microsoft Graph Nested Email Attachments in Azure Automation

Learn how to handle nested email attachments using Microsoft Graph API in Azure Automation and resolve issues caused by regex mismatches.
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This video is based on the question https://stackoverflow.com/q/79352579/ asked by the user 'Lukas Østergaard' ( https://stackoverflow.com/u/15955062/ ) and on the answer https://stackoverflow.com/a/79420277/ provided by the user 'Lukas Østergaard' ( https://stackoverflow.com/u/15955062/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

When automating email processing with Microsoft Graph API in Azure Automation, handling nested attachments like emails containing Excel or ZIP files can be challenging. After renewing your MS Graph secret, you might encounter issues where your script fails to recognize or download these nested attachments correctly.

The Problem

Direct attachments (e.g., Excel files) download fine.

Nested attachments (emails containing attachments) are not handled correctly.

Matching boundaries and content disposition headers in nested MIME parts fails.

Debugging is difficult because Azure Automation's test pane limits output.

The script may run indefinitely without obvious errors.

Understanding the Attachment Structure

Nested email attachments are typically MIME multipart messages. To extract files:

You must parse the MIME structure correctly.

Identify boundary strings from Content-Type headers with regex.

Detect file attachments by parsing Content-Disposition headers.

Decode base64 content to retrieve original files.

Common Pitfall: Outdated or Incorrect Regex

The root cause is often regex changes or mismatches between Microsoft Graph API versions or response formats after secret renewal or API updates. This prevents finding the multipart boundaries or filenames properly.

Modern and Reliable Approach

Verify returned attachment content:

Log or export $v.Result.Content for sample responses (outside Azure Automation if needed).

Update Regex Patterns:

Ensure regex matches exact header formats.

Example for Content-Disposition must capture filename correctly:

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Adjust boundary extraction regex similarly.

Graceful Parsing:

Check regex match results before processing.

Add error handling for no matches.

Base64 Decoding:

After isolating base64, decode content robustly using:

[[See Video to Reveal this Text or Code Snippet]]

Testing & Debugging:

Use local PowerShell or Azure Functions where output is easier to inspect.

Once stable, deploy back to Azure Automation.

Summary

If your Microsoft Graph API calls to fetch nested attachments fail after secret renewal, review your regex patterns. They may need updating to match new API output formats. Use precise regex to extract multipart boundaries and content-disposition filenames. Decode base64 content carefully. This approach resolves issues where scripts hang or fail silently when processing nested email attachments in Azure Automation.

Additional Tips

Always test regex with actual API responses.

Modularize code to isolate parsing logic for easier testing.

Consider libraries or SDKs that handle MIME parsing if available.

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By following these steps, you can reliably extract nested Excel or ZIP attachments from emails using Microsoft Graph API in Azure Automation.