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I'm facing some strange behavior with Outlook. Outlook seems to changes the attached files that I send. The content of the file remains the same but the file size increase by 1-3 Kb (differ from one file to the other).

Below more details regarding this issue.

Problem description:

In Outlook 2003, sending an email with an attachment modifies the sent attachment. Files are increased by 500-1000 bytes

More details:

  • This happens only with Microsoft Office files.
  • This happens even if the mail is sent to myself.
  • The Sent folder contain a copy of the sent email where its attachment has been modified.
  • Files are not modified if using the attached file extension is changed (from . Doc to . Bin for example)
  • I an running Windows XP OS, Outlook 2003 SP3.
  • I made sure that all the option tools->email options-> advanced-> Add properties... Is set to off.
  • Right clicking for properties, details provide no new information.
  • comparing the before file and after file reveals that outlook changed a few bytes in the beginning of files and added lots of bytes at the end of the file. I notice the words "root entry" and "summery information...".

    1. Does anyone know why outlook changes the files?
    2. Other than DOC, XLS, PPT are there any more types of file that are altered.
    3. How can it be configured to stop this behavior.
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migrated from May 29 '11 at 14:15

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Why do you want Outlook to stop altering the file size? – Flauwekeul May 29 '11 at 12:28
Are you using any third party software linked to Outlook like Metadata Assistant? Workshare or Deltaview? Even Hummingbird DM? Outlook should not add anything to the document itself because it has to be opened/saved to do so... I'm sceptical that O2003 does that. Let me know! – r0ca Jun 1 '11 at 13:07

It's probably outlook "inlining" metadata from the file (e.g. right click, props, details). This data is stored in an alternate stream on the file system and is not reported in the file size (add some metadata using the properties dialog, its reported size won't change on disk).

You should be able to confirm this by adding a large "comment" to the file and comparing sizes.

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