Error: Outlook Data File Has Reached its Maximum Size…

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Symptom:  Upon opening or using Outlook, an error pops up containing the  following message:

“(path-to-.pst-or-.ost) has reached its maximum size. To reduce
the amount of data in this file, select some items that you no longer need,
then permanently (shift + del) delete them.”

Problem:  There are a few different reasons that this can occur.

  1. Your ANSI-encoded .pst or .ost file is larger than or approaching the 2Gb limit.
  2. Your Unicode-encoded .pst or .ost file is larger than or approaching the 50Gb limit.  (whoa!)
  3. There is a registry setting or policy in place that has changed the default limits.


The solution to this problem will depend on which of the scenarios above is affecting the Outlook data file in question.  Here is how to find that out:

Determining The Type of Outlook Data File

  1. With Outlook closed, go to Start->Control Panel->Mail
  2. Click “Data Files…”
  3. Double-click the data file in question.
  4. If the “Microsoft Exchange” window appears, than the file is an .ost.  Click the “Advanced” tab.  At the bottom of the window will be a message declaring the “Mailbox Mode” as either Unicode or non-Unicode.  Take note of which mode it indicates.
  5. If the “Personal Folders” window appears, than the file is a .pst.  Look for the box labeled “Format:”.  If the value of that box is “Personal Folders File (97-2002)”, then the file is ANSI.  If the value is simply “Personal Folders File” then it is Unicode.  Take note of which it is.

Locating the Outlook Data File

  1. Make sure that Hidden Files are not hidden.  To do this, in any Explorer window go to “Tools->Folder Options…” then click the “View” tab and select the radio button for “Show hidden files…”  In Windows 7, if there is no menu bar with a “Tools” option, try hitting the ALT key to make it appear.
  2. In Windows 2K/XP, the default location will be C:\Documents and Settings\-your-username-here\Local Settings\Application Data\Microsoft\Outlook\
  3. In Windows Vista/7, the default location will be C:\Users\-your-username-here\AppData\Local\Microsoft\Outlook\
  4. If Outlook is being used with an Exchange server, there will be one or more .ost files in this folder.  Otherwise, there will be one or more .pst files.
  5. Check to see if the size of the .pst or .ost file currently used by Outlook is approaching the limit set by the file type that was discovered in step 5 above.  For example, if the file is ANSI the limit is just shy of 2Gb, if Unicode the limit is just shy of 50Gb.  If the file is ANSI and the version of Outlook is 2003 or newer, the file can be converted to Unicode by following the steps below.  If the file is Unicode and is hitting the limit, steps must be taken to shrink the .pst or .ost file such as archiving old items or deleting unnecessary items.

Converting an ANSI-encoded .pst file to UNICODE

  1. Create a new Outlook profile with a new, empty .pst file.  If Outlook is newer than 2003, the new .pst file will be Unicode by default.
  2. Import the old .pst file into the new one.

Converting an ANSI-encoded .ost file to Unicode

  1. Disable “Cached Exchange Mode”
  2. Rename the .ost file in question to “outlook.old”
  3. Open Outlook, then close it.
  4. Re-enable “Cached Exchange Mode”
  5. Outlook should now rebuild the .ost file in a Unicode format with data from the Exchange server.  Depending on the size of the mailbox this could take a while.

File is Already the Correct Type and Is not Approaching the Above Limits

If this message is popping up even though the .pst or .ost file is not approaching the limit appropriate for its encoding, there may be custom policies or registry keys changing the default MaxFileSize and MaxLargeFileSize attributes.  Check out this MS KB article on the subject that includes paths to the keys for different versions of Outlook as well as information on group policy setting that can affect Outlook data file enoding:  http://support.microsoft.com/kb/832925



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  1. navid says:

    khoob bood

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