Managing Reference Attachments in MSG Files

MSG files, commonly used by Microsoft Outlook, store email messages along with their attachments, recipients, and metadata. While standard attachments embed content directly within the email, reference attachments link to external files, such as network-shared documents or web-hosted resources.

In this article, you’ll learn how to work with reference attachments in MSG files using Aspose.Email for .NET. We’ll cover how to identify, read, and add reference attachments programmatically in C#. This approach is essential for managing large files efficiently and dynamically linking external resources.

Aspose.Email for .NET: Working with MSG Files and Attachments

Aspose.Email for .NET is a dedicated email processing API for .NET developers. It provides functionality for reading, creating, and modifying MSG files, along with handling attachments, calendars, and email protocols like IMAP, POP3, SMTP, EWS, and Microsoft Graph.

When working with reference attachments in MSG files, Aspose.Email simplifies tasks such as detecting, extracting, and adding these attachments. Instead of manually parsing MSG structures or relying on Outlook, developers can use the API to access MAPI properties, retrieve external file links, and manipulate email content programmatically.

To get started with Aspose.Email for .NET, you can install it via NuGet with the following command:

PM> Install-Package Aspose.Email

Once integrated into your project, you can leverage the API to work with MSG files and attachments in a structured and efficient manner, enhancing your email management capabilities in C# applications.

How to Identify Reference Attachments in MSG Files

Reference attachments in MSG files can be identified using the IsReference property of the MapiAttachment class. Unlike standard attachments, these are pointers to external files rather than embedded objects. The code sample below will show you how to detect reference attachments in an MSG file. It loads an MSG file and checks the IsReference property for each attachment, allowing you to process reference-based attachments accordingly.

Steps:

  1. Load an Outlook message using the MapiMessage.Load method providing the file name.
  2. Iterate through all attachments present in the msg.Attachments collection.
  3. Check if the current attachment is a reference using the attachment.IsReference property.
  4. If the attachment is a reference, print a message indicating that a reference attachment is detected, along with its display name.

Code sample:

Reading Properties of Reference Attachments

Reference attachments are determined by the IsReference property and their file path or a web link, based on the PidTagAttachMethod MAPI property. Below are the key values that indicate reference attachments:

  • 0x00000002 - afByReference: The attachment is identified by a fully qualified file path, accessible to recipients with shared access to the file server.
  • 0x00000004 - afByReferenceOnly: The attachment is identified solely by its fully qualified file path.
  • 0x00000007 - afByWebReference: The attachment is identified by a web link, with the PidNameAttachmentProviderType specifying the web service API handling the attachment.

If the attachment does not match these criteria, the IsReference property returns False.

To extract reference attachment details, including the original URL, use the following approach:

In this example:

  • AttachmentOriginalUrl retrieves the original web link if the attachment is referenced by a web URL.
  • AttachmentProviderType indicates the web service API handling the attachment.
  • AttachLongPathname provides the full file path if the attachment is referenced by a file path.
  • AttachMethod returns the attachment method, helping determine the reference type.

Using this approach, you can effectively handle reference attachments by reading their properties and accessing their external content, whether it’s a web link or a file path.

Adding Reference Attachments in MSG Files

You can add reference attachments using the MapiAttachmentCollection.Add method which includes an overload to add reference attachments and the ReferenceAttachmentOptions class which allows you to specify details such as the attachment’s URL, the provider link, and the provider type. This approach allows you to specify an external file or web link without embedding the content.

Here’s how you can add a reference attachment to an MSG file:

The ReferenceAttachmentOptions constructor accepts three parameters:

  • Attachment URL: The direct link to the referenced file.
  • Provider link: The URL of the web service or file provider.
  • Provider type: A string specifying the web service API handling the attachment (e.g., “GoogleDrive”).

The MapiAttachmentCollection.Add method then adds a reference attachment named “Document.pdf” with the specified options.

Using this method, you can include references to external files or web links in your MSG messages without embedding the content directly, making your messages more lightweight and flexible.

Conclusion

In this article, we explored how to manage reference attachments in MSG files using Aspose.Email for .NET. We covered methods to identify reference attachments, extract their properties, and add new ones programmatically. Unlike standard attachments, reference attachments link to external resources, reducing email size and improving accessibility.

By integrating these features into your .NET applications, you can efficiently handle large files, maintain dynamic content, and optimize email storage. Whether you’re automating email workflows or managing external links in MSG files, Aspose.Email for .NET provides a flexible and powerful solution.

For more resources, check out the following:

  • API Reference – Explore detailed documentation on available classes and methods.
  • Developer Guide – Step-by-step tutorials and code examples to help you get started.
  • Support Forum – Ask questions, share insights, and get help from the community.
  • Blog – Stay updated with the latest features, best practices, and tutorials.

See Also