Original KB number: 2800895
We do not recommend that you change the default location of your Profile folder for Microsoft Outlook 2016 for Mac, or your Identity folder for Microsoft Outlook for Mac 2011 to an external hard disk or to a network. Additionally, using a mail identity or profile that is located on an external hard disk or on a network is not supported in either version of Outlook for Mac.
Items from an Exchange account are stored in the Outlook cache. If this cache becomes corrupted, it may cause synchronization problems with the Exchange server. To solve this problem, you can empty the cache in Outlook so that Outlook 2016 for Mac can download. Download and open the Outlook Reset Preferences tool. Click the Reset Now! This closes Outlook if it's open, and then resets the preferences to their default settings.
Outlook 2016 for Mac caches your mail items in a profile in your home folder at the following location:
~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles
Outlook for Mac 2011 caches your mail items in an identity in your home folder at the following location:
~/Documents/Microsoft User Data/Office 2011 Identities
Like Microsoft Entourage for Mac 2008, Outlook 2016 for Mac and Outlook for Mac 2011 are intended to be purely locally cached mail clients. Changing the location or using a mail identity that is located on an external hard disk or a network is not supported.
Lately I’m having some sync issues with my mailbox. For instance, I see several new emails in my mailbox when I login to webmail which I don’t see in Outlook.
Also, it looks like the entire month of June has gone missing in Outlook but the emails are luckily still available on the server.
Is there any way to get Outlook to sync or download these emails again?
Corruptions in the cache are rare (especially for Exchange based accounts) but can still happen under various circumstances like an unexpected shutdown or crash of your computer or Outlook.
In these cases, it might be best to reset the local cache of Outlook and let it rebuild. The process is fairly simple to perform but make sure you do some checks first.
The first thing to check is whether all messages that you expect to be on the mail server (via webmail) are still there as well.
You don’t actually have to check each and every message. With sync issues you are usually missing emails in Outlook and not in webmail. However, you do want to pay a bit more attention to folders you recently moved emails into and your Sent Items folder.
If you are missing any emails on the server, either drag & drop them out of Outlook and into a folder in your Documents folder (via File Explorer) to save them as msg-file or export/copy them to a pst-file.
Both methods will allow you to restore these items to Outlook and/or the mail server later on.
Drag & drop messages from Outlook into File Explorer to create msg-files.
If any of your folders of your mailbox in Outlook are marked with “This computer only”, you’ll need to copy or export the contents of these folders as well before resetting your cache.
These folders are likely to exist when you only have an IMAP account configured in Outlook 2013 or Outlook 2016.
A good method to find these folders is by switching to the Folder List Navigation in Outlook (keyboard shortcut CTRL+6). Common folders that are marked with “This computer only” are;
Extra Tip!
Configure Outlook to store the “This computer only” folders within a pst-file so you won’t risk losing them and also making it easier to back them up. For more details see: Don’t risk losing your Contacts and Calendar when using IMAP in Outlook 2013 or Outlook 2016
Now that all your unique data from the cache is backed up, you can reset the cache in the following way;
C:Users%username%AppDataLocalMicrosoftOutlook
.old
so it will now be called like; <filename>.ost.old
Opening the file location of an ost-file via the Data Files tab in Account Settings. (click on image to enlarge)
If you backed up any data in step 2, then you restore these items after Outlook has finished syncing all your data.
If you backed them up as msg-files, then you can simply drag & drop these files back into Outlook.’
If you created a pst-file, then you can connect to this pst-file in Outlook via;
You can then drag & drop these items to their correct folders within Outlook.
After a sync interval, these items should be available again within webmail as well, unless the items are stored within “On this computer only” folders.