Bloated OST file: 19GB


Anonymous Bosch

I have a user with a 19.0 GB .OST

Outlook says his mailbox is around 1.0GB, which matches what the Exchange
server says (or thereabouts).

I renamed and recreated his .OST a month ago, and once before that as well.
The problem keeps coming back. This is the third time this user has
experienced this error.

This is an Exchange 2003 environment. This user has Vista SP1 and Office
2007 SP1. He is set up to auto-archive every 14 days anything older than 4
months ago. The user is also using Cached Exchange Mode. He does not use RSS

I have other users with this error as well, and so far the only solution is
to recreate the .OST. But in this case, it does not seem to be a permanant

I have read that sometimes Outlook will not actually remove allocated space
from the .OST when items are deleted. Could this be an issue? If so, any

Also, I have done some tests on my system with similar specs (SP1 for Vista
and Office 2007) and I get a similar error: it seems that when Outlook
archives, it does not release the space that the OST is using. So, in my
example I had a 150MB OST, and a 6MB archive to start. After archiving
EVERYTHING, my OST was still 150MB, but my archive was 135MB or so.




Diane Poremsky {MVP}

1. are there a lot of sync error messages?
2. the ost should compress automatically when you have about 20% free 'white

** Please include your Outlook version, Account type, and Windows Version
when requesting assistance **



Do these users have Personal Folders (PST) they are using as well?

You stated that, "...have a user with a 19.0 GB .OST", but then you indicate
on the next line that Outlook says his mailbox is 1GB and Exchange reports
the same information. Is this a correct statement and if so where are you
seeing the 19GB file size?

We are quickly approaching these same issues that you are faced with and so
in researching this issue a few weeks ago I came accross the following
article in the MS KB. I have reservations though about the implications of
allowing the OST and/or PST files to go beyond the 20GB limit.

Please repost and let me know if you decide to take these steps and allow
the file size to increase. We will be facing this same decision not to far
in the future. I can only hope the PST files will not suffer from
corruption or other issues as I have experienced in the past...

Good Luck...

Anonymous Bosch

Mailbox file sizes:
When logged in to the Mail server: 1.04GB mailbox size
When viewed in Outlook (mailbox, properties, foldersize): 1.02GB total for
all folders
OST size Via Explorer: 19.2GB
(in C:\Users\<username>\AppData\Local\Microsoft\Outlook\outlook.ost)

So the users ACTUAL mailbox size is around 1GB, however somehow the OST is
getting bloated to 19GB. It seems to be related to the archive process.

YES, the user has some PST's, but they are all under 100MB, and are not
being archived with the OST file.

I have to wonder about mailbox corruption, especially since we have already
re-created the OST in the past, but the "bloating-error" keeps reappearing.

Other thoughts?

Anonymous Bosch

The user has 30-40GB free on a 160GB hard disk. (So, roughly 20%, yes).
However, I do not know if this is a "compression issue" since apparently the
user's mailbox is only 1GB. It does not really explain the difference in size
on server vs on the local computer.


Diane Poremsky {MVP}

Free white space is not about available space on the hard drive - when you
empty the deleted items, it will compress when the free space (aka white
space) within the ost is greater than 20%.

Check the sync folders - are there a lot of sync error messages?
Have you tried a new profile? Close outlook and go to control panel, mail
and make a new profile.

** Please include your Outlook version, Account type, and Windows Version
when requesting assistance **



Anonymous Bosch

On this system we have deleted approximately 18,000 sync error messages. I
have also once again re-created the OST. Hopefully this will solve the issue.
If not, I will be back.

Thank you for the advice.

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