Funny 'Export-Mailbox' behaviour

I'm using Export-Mailbox to export some data into PST in various occasions, like when the user is leaving or to slim some users mailboxes.
I noticed something strange recently.
When I run the same command with same parameters, I get different PST sizes !
I was exporting 'Inbox' contents for a specific month for one user, I did it 3 times, and 3 times the file size was different.

When I attached the PSTs to outlook, I've got the same number of items, I checked few attachments and it all looked fine.

I don't remember exactly what the file sizes were so lets assume 1st was 1GB, 2nd was 2GB and 3rd was 3GB.

I thought that the size difference would be just empty space so I compressed the 2nd one and to my surprise, after compression the file was still bigger than a 1st one.

Can someone try to explain me that behavior ?

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Will SzymkowskiSenior Solution ArchitectCommented:
When a typical export is completed it gives a detailed list of all of the items that were exported. When you export the same mailbox different times do these reports match up? Also are there any flags to skip corrupted mailbox items?

tp-it-teamAuthor Commented:
Well, not really, there is no detailed report. Here is what I get (I skipped first few lines which tell server name, user, location in the AD etc).

SourceGlobalCatalog              : DC
SourceDomainController           :
TargetGlobalCatalog              : DC
TargetDomainController           :
TargetMailbox                    :
TargetServer                     :
TargetDatabase                   :
MailboxSize                      : 5488339KB
IsResourceMailbox                : False
SIDUsedInMatch                   :
SMTPProxies                      :
SourceManager                    :
SourceDirectReports              :
SourcePublicDelegates            :
SourcePublicDelegatesBL          :
SourceAltRecipient               :
SourceAltRecipientBL             :
SourceDeliverAndRedirect         :
MatchedTargetNTAccountDN         :
IsMatchedNTAccountMailboxEnabled :
MatchedContactsDNList            :
TargetNTAccountDNToCreate        :
TargetManager                    :
TargetDirectReports              :
TargetPublicDelegates            :
TargetPublicDelegatesBL          :
TargetAltRecipient               :
TargetAltRecipientBL             :
TargetDeliverAndRedirect         :
Options                          : Default
SourceForestCredential           :
TargetForestCredential           :
TargetFolder                     :
PSTFilePath                      : z:\user_inbox_201109_4.pst
RsgMailboxGuid                   :
RsgMailboxLegacyExchangeDN       :
RsgMailboxDisplayName            :
RsgDatabaseGuid                  :
StandardMessagesDeleted          : 0
AssociatedMessagesDeleted        : 0
DumpsterMessagesDeleted          : 0
MoveType                         : ExportToPST
MoveStage                        : Completed
StartTime                        : 03/10/2013 12:39:17
EndTime                          : 03/10/2013 12:56:42
StatusCode                       : 0
StatusMessage                    : This mailbox has been exported to the PST fi
ReportFile                       : C:\Program Files\Microsoft\Exchange Server\L

There is nothing to skip messages, and when I attach these psts to outlook, they all have the same number of items.
Will SzymkowskiSenior Solution ArchitectCommented:
What you could try to see if you can get more detail is export 2 copies of the PST files attach them both to an Outlook session and from there rigth click, properties, Folder Sizes button and compare them at the folder level.

Also, do you get the same results when you do different mailboxes or is it just one mailbox in question?
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tp-it-teamAuthor Commented:
When I'm checking the folder size, its the same.
Doesn't matter which mailbox I'm working on.
Will SzymkowskiSenior Solution ArchitectCommented:
I have tested this in my environment and in my test lab using the the same command export-mailbox -identity "name" -PSTFolderPath c:\path. I have had same export results everytime.

I have tested this with new accounts seasoned accounts. large, small and all of the PST files export the same size.

When you are running this command are you doing it from the same workstation or doing it directly on the server? Have you tried running the command from a different computer? Maybe there is something on the machine that is messing with the file sizes?
tp-it-teamAuthor Commented:
I'm doing it on the workstation. Its not possible to do it on the server as it requires 32bit environment.

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tp-it-teamAuthor Commented:
Problem unresolved. Its not that important actually so I'm not interested in continuing investigating it.
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