Size Reduction when Converting MSG Files to PST

Aspose.Email Product Family
1

Hello Aspose Support Team,

We are noticing a recurring issue with size reduction when converting MSG files to PST using Aspose.Email.

For example:
Case 1: 109 msg files totaling 6.09 MB result in a PST of only 5.6 MB.
Case 2: A set of .msg files totaling 1023.23 MB results in a PST of only 874.3 MB.

We are not using the setUseBodyCompression(true) option during conversion.

Could you please explain why there is such a significant reduction in size during conversion? Is this expected behavior, and what factors contribute to this difference?

Thank you for your support.

Best regards,
Deepraj

2

@deepraj.majalikar

Hello Deepraj,

The size reduction you are experiencing when converting MSG files to PST using Aspose.Email can be attributed to several factors:

  1. File Format Differences: MSG files are individual email files that may contain additional metadata and attachments, while PST files are designed to store multiple emails and their associated data in a more compact format. During conversion, some of this metadata may be optimized or removed, leading to a smaller file size.

  2. Compression: The PST format may apply internal compression or optimization that reduces the overall size of the data stored, even if you are not explicitly using any compression options.

  3. Redundant Data: MSG files may contain redundant or unnecessary data that is not carried over to the PST format, contributing to the size difference.

This behavior is generally expected, and the factors mentioned above can lead to significant size reductions during the conversion process. If you have specific requirements regarding the size of the output PST files, consider reviewing the available options in the Aspose.Email library that could influence the conversion process.

Best regards,
Aspose Support Team

3

I have a follow-up question:
Is there a way to make the output PST size more consistent with the total size of the input MSG files?

Specifically:

  • Are there any options or settings (e.g., disabling internal optimizations or compression at the PST level) that would preserve the data size more closely?
  • If not, is there a recommended approach to ensure that the PST size does not differ significantly from the MSG total size?

We want to confirm if this difference can be controlled, or if the size reduction is inherent to the PST format and unavoidable.

4

Hello @deepraj.majalikar,

The difference in size between individual MSG files and the resulting PST file is expected behavior and is primarily due to the way data is stored in the two formats:

  • MSG files store each message as a separate compound file with its own overhead.

  • PST files, on the other hand, are designed as a single container that stores messages in a more compact, indexed, and optimized way. Redundant or repeated structures are reduced, and internal storage is more efficient.

Regarding your questions:

There are no settings that disable these inherent optimizations or force the PST file to be closer in size to the sum of the MSG files. PST always uses its own storage mechanism and may appear smaller than the MSG total size.

So, this size difference cannot be controlled. The smaller PST size does not indicate data loss, it reflects different storage model.