Outlook 2010 - Multiple devices configured for same Exchange account but different .OST file sizes

Outlook sync problems usually points towards some sort of networking issue. Have you tried updating the NIC drivers on all the devices as a first step? It's unlikely that this is the issue though as you say the sync problems are happening on all three machines, but nevertheless it's always nice to have up-to-date drivers :) - just make sure you get the drivers from the laptop manufacturer's website.

The mailbox may also be potentially corrupt. Try running the New-MailboxRepairRequest command on the user's mailbox to see if it fixes the issue:

New-MailboxRepairRequest -Mailbox user@company.com -CorruptionType SearchFolder,AggregateCounts,ProvisionedFolder,FolderView

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Keep in mind that the user won't be able to access their mailbox while the repair runs. To find out more about this command please see this article: https://technet.microsoft.com/en-us/library/ff625226(v=exchg.141).aspx

Thanks a bunch, I will try to get this done today and post an update.

Not!
If you go to the More Settings option in accounts and then the advanced tab, the default is to delete the email from the server when it is received.  Check the box to leave a copy on the server and I generally check the box to remove when deleted items are removed.  You will need to do it on all 3 systems.
What is happening is that, when he receives an email on one device, it is then removed from the server so every inbox is different!

Thanks all. I did not have the opportunity to check any if these sugestions. I'll do my best to get it done within the next few days and post an update.

@VB ITS: I updated the NIC drivers with no noticeable change in anything afterwards. Network problems may be a reason so will ask my networking guy to take a peek. I have not had a chance to kick the User off from using email so I can try the repair of the mailbox. Will provide an update when completed.

@DavisMcCarn: Thanks for the suggestion but unfortunately those options are not available to me. The only options I have under the 'Advanced' tab is to "Open additional mailboxes" , "Cached Mode Settings", and "Outlook Data File Settings". None of those options have anything related to what you state.  

@weinberk: Thanks for the clarification on why they would be different in size. Yes, I uninstalled everything on all three machines and then reinstalled from scratch, including moving the original .OST to a different folder so as not to re-use the same file. No activity was happening in the mailbox during this uninstall/reinstall since I was able to do this during a meeting the User had. Upon completing re-installation I loaded the mailbox to all three devices one at a time. All new .OST files are different in size by multiple gigs.    

Also, I performed all updates to Windows and the Office Suite to rule that out.

Apparently, you are right; the option to leave a copy on the server is missing for cached exchange accounts.  However; it is still the root of your problem and the only fix seems to be to change all 3 PC's to a pop3 account so you will have the option.
Three, completely different, inboxes is enough to drive someone crazy!

Different by multiple GB is different than I was talking about.  I was guessing a couple MB difference.  Forget everything I was saying.

I just setup an account on 2 different Windows 8.1 boxes, each under Outlook 2013  to see what I could find.  To my immense surprise, after syncing completely, one OST is 164mb and the other is 560mb.  Same account, same data.  I have ABSOLUTELY no idea why that would be.  This is running off of an Exchange 2013 server.    Only thing I can now guess is something to do with how the OST is indexed using the built in Outlook / Windows indexing service.  

Now, we're not having any trouble with that server and the account that I put on the 2 machines is fine, but I, like you, find it odd that the 2 OST files would be so different in size.    I'm not worried, but I still find it curious.

And again @Davis, I think you are way off base here.  Exchange is a server based  solution.  Yes, you can enable pop, but there's generally not a real reason to.  It operates quite well with multiple devices keeping a single account in sync (WIndows Mobile, Android, iOS, OWA, Outlook).

I

As long as you use IMAP, yes; but, an Exchange account deletes emails received on that device when they are received which is fine as long as you don't have multiple devices.

@DavidMcCarn.  I'm not sure what you're thinking of, but this simply is not true.  

Under normal operating circumstances with Outlook Anywhere,  RPC, RPC over HTTP(s), etc, mail stays in sync with the server.  Cached mode or not, mail stays on the exchange server unless you're using pop and tell it to delete upon download to the client.

@Davis: I cannot change the account type as a viable solution. I will, however, bring this up as a suggestion and if allowed I can try it and see what happens.

@weinberk: Yea, I don't know why either but the User in question has a real good way of putting me in a pickle and demands exact, verifiable answers for all questions. In this case, I noticed the size differences and since I did not have an answer right then I am now tasked with finding out why they are so different in size, and whether or not that difference is why the User sees the loss of emails among devices and the numerous synch failure emails. I have no problems with the Server or anything else, and it could just be the way all devices are synch'ing to the Server that is the actual problem.

If this were a network problem as suggested by 'VB ITS' I suppose this issue would be seen by other staff, but I am not ruling that out as a possibility. My network guy will peek at that when he can.

Does anyone here think it could be related to (4) devices trying to sync the same Mailbox? I do know that having multiple devices sync'd can cause all sorts of sync errors and failures, but shouldn't everything eventually sync? I mean, I believe the sync continues until it succeeds, so even receiving a failure notice I have seen the failed email appear properly in a short time, once the connection is solid and an update occurs. Could this really be the issue?

I have 5 devices syncing my Ex 2013 mailbox, 2 Outlook 2013, 1 Outlook 2010, and 2 Android devices.  The outlook OST's are all significantly different in size, but I see no sync issues, everything seems to be everywhere.

(oh, and I just re-read the OP, sorry that I originally missed the huge difference in OST size)

I know there are sync issues and calendaring isn't working.  I wonder if that might be something separate from missing emails.  When you say some emails "can't be found" do you mean via search or by just going to the date/time that the message is known to have been delivered?  If search, maybe it's an indexing problem?

Thanks a lot for your help and clarification guys. I have not beem able to run the repair yet but will.
The link and info on the .OST is very helpful too.

@VB ITS: thanks for backing me up on the crazy @Davis posts.  Just totally wrong, insistent, confident, and totally wrong.

@Machienet:  Assuming we've addressed everything, accept (the hopefully helpful) answers and close this?

I am performing the repair on the mailbox tonight. So far everything else suggested has not helped. I will be posting an update tomorrow about the repair, but I may need to keep this open until the User confirms whether or not the issue is gone.

Will the repair process delete anything? Should I make a backup first?
Egad! How do I back up the User's mailbox?!

Thanks for the patience!

4 ways to backup the mailbox that I can think of:

1) in powershell on the server do something like:
New-MailboxExportRequest -Mailbox THeUsername -FilePath "\\SERVERNAME\AShareName\TheUserBackup.pst"
That's for exchange 2013

2) Export using ECP

3)  not-elegant-but-it-works-way:  Create PST on an Outlook machine where you know all data resides.  Copy all folders, contacts, calendar, tasks, notes, etc to the PST.  COPY do not move.  Save PST

4) use server side software like BackupExec on the exchange server

Thanks guys. Update later or tomorrow.

Ran the repair, went quickly and smoothly. Verified it ran by checking the Event logs. Got both the start and the completed events. Was done in mere moments. Hard for me to believe it actually scanned anything.

Does it usually run that fast?

You guys answered my question as best as possible and gave more suggestions for repairs in case that was the issue.

I'll probably update this on how the repair went (see how things go) but the original question was answered.

Thanks.

- Cheers!

OK, good news Gents!

The User notified me today that 30 unread emails from before noon yesterday appeared in her devices this morning. They were all marked as Unread, and they were not there before.

I think the repair fixed some issues, even though I saw no Events stating so.

Thanks again!