Users may notice that after their scan/s on .PST/OST files are completed, the reported "Scanned Bytes" may not be in line with the size of the actual file.
For example, one may have scanned a 10GB .PST file successfully but it is reported that only 2GB worth of data has been scanned in total. This may lead to the misunderstanding that the scan wasn't complete when in fact, it was.
A .PST/OST file is essentially a database file that contains a lot of indexes and space between records, especially if there is fragmentation within after prolonged usage (ie. records being deleted and added regularly over a large span of time).
Furthermore, the .PST/OST file stores multiple copies of email in different formats for rendering purposes. Our scanner will pick the simplest format and scan that since we are only looking for text data.
Additionally, emails typically contain a large amount of image data in advertisements/email signatures/company logos/etc. We will perform OCR scanning on these if OCR is enabled, but even so, an image that only has 100 bytes of text might be 128,000 bytes in (total) size.
With these factors considered, even if the total amount of data actually scanned isn't in line with the .PST/OST file size, please rest assured that the scanner did indeed perform a "complete" scan.
It is good practice to compact your .PST/OST files regularly, especially after a large cleanup of emails.
You may refer to this article for instructions on how to compact your Outlook Data Files.
All information in this article is accurate and true as of the last edited date.