What do Synchronization Log error messages mean in Outlook 2010/13?

Sometimes you may receive an email, apparently from yourself, with the Subject line "Synchronization Log:" and the content may look something like this:

12:49:39 Synchronizer Version 14.0.7108

12:49:39 Synchronizing Mailbox ‘Your Mailbox’

12:49:39 Synchronizing local changes in folder 'Inbox'

12:49:39 Uploading to server ‘server.yourcompany.com’

12:49:39 Synchronization of some deletions failed.

12:49:39                  [0-130]

12:49:39            1 item(s) deleted in online folder

12:49:39 Done

Your name (or the name of the mailbox) would be shown where we have used 'Ann Other' as an example here.  The time shown on the left of the lines in the message indicate the time the synchronizer log entry was made, and will probably match the time the message was sent to you.
This is probably happening if you're using Outlook in Cached Exchange Mode and there is a problem with the caching file on your computer.  You may also receive apparently false 'mailbox full' warnings.

The simplest solution is to switch off Cached Exchange Mode (we do not recommend using CEM anyway).  To do this, follow the instructions

If Outlook 2010 or 2013 is using Cached Exchange Mode, although sometimes useful, it causes a number of side-effects which can be detrimental.  See under the heading 'Effects of using Cached Exchange mode' below.
To check if Cached Exchange Mode is in use, follow the instructions below. Step 1 depends on which version of Outlook you have:

1. Click the File menu tab, then click the Account Settings button, then click on Account Settings... in the drop-down menu.
2. Click to select the required account (there may be only one) in the list shown.
3. Click on Change....
4. If the Use Cached Exchange Mode checkbox is ticked, Cached Exchange Mode is in use by your Outlook profile.

To switch off Cached Exchange Mode, click to remove the tick-mark from the Use Cached Exchange Mode checkbox, then:

1. Click the Next button.
2. Click Finish.
3. Click Close to close the Account Settings dialogue box.

Effects of using Cached Exchange Mode

Having Cached Exchange Mode switched on for your installation of Outlook means that a copy of every email message is downloaded and kept on your computer.   It can also affect how soon you see changes made on the Exchange system, such as changes to the Global Address List (staff address book).   It can also adversely affect Outlook's message searching facility.  For most users we recommend that Cached Exchange Mode should be turned off, but if you really need to keep a copy of your email (for example if you have a laptop and want to be able to search old emails while you are offline), you can use this mode.   Please be aware however that if your account has only recently been transferred to Exchange and you have a lot of email, it could take several hours for Outlook to download all of your mail the first time you use it.