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Fixes for Outlook downloading way too much data

Sometimes Outlook for Windows can download a lot of data that it doesn’t mean to.  When we say ‘a lot’ we mean many gigabytes, sometimes far more than the size of the mailbox, which makes no sense at all. Here’s some options for fixing the problem with tips for using Outlook more efficiently.

Is Outlook to blame?

Make sure that Outlook really is the program gobbling up all the bandwidth.  Just because Outlook is a major program doesn’t mean it’s necessarily to blame for high data use.  It could be Windows itself or some app running in the background.  Use Task Manager or Resource Monitor to identify what program or process is using up your Internet data.

Outlook Cached Mode

If Outlook is using up a lot of network data, there are a few possibilities. These apply to Exchange Server / Outlook.com mailboxes using Cached Mode (the default).

Cached Mode works by keeping a copy of recent or all data on your computer (in an OST file).  After first setting up a mailbox, Outlook will use a lot of bandwidth copying data from the server to the local machine.  That’s normal but should settle down once everything is copied over.

If you increase the amount saved on the computer, that will also force more copying from the server.  We recommend saving more than Microsoft’s default, downloading all past email, assuming you have enough disk space.

Outlook gets confused

What happens occasionally and we’ve seen ourselves is Outlook downloading excessive Gigabytes of data … far more than it needs to.   For example, downloading over 100GB for a 10GB mailbox.  Something is clearly wrong with Outlook copying the same information over and over again.

What’s wrong?  Is anyone’s guess but most likely there’s an error in the OST file which stores Outlook data on the computer.  OST/PST files are large complex database files which can get errors.  Outlook can cope with most of these problems but occasionally it can’t.

There are two ways to check and fix an OST Outlook file.  Check and fix the OST with ScanPST or totally rebuild the OST from scratch.

ScanPST

ScanPST.exe is a tool installed with Outlook.  It will check an Outlook data file and attempt to repair it, with mixed success.

It’s officially called the “Microsoft Outlook Inbox Repair Tool” but is known almost universally as ScanPST.  Despite the name, these days ScanPST works for both PST and OST Outlook data files.

Force Outlook to start again

The alternative is to force Outlook to recreate the entire mailbox connection and make a completely new OST file.

Microsoft doesn’t recommend using ScanPST for Exchange Server/Outlook.com mailboxes because they suggest deleting the data file and downloading an entirely new data file. Redownloading is OK if you have a fast and limitless Internet connection, but many people don’t have that option.  Redownloading isn’t an option for IMAP or POP connections.

You can limit the data downloaded by adjusting the Cached Exchange Mode setting to the left, maybe a month.  Later, when you’re on a better connection, extend the data saved to a year or more.

There are two ways to recreate a mailbox connection, depending on whether there are multiple mailboxes setup in the one Outlook profile

(An Outlook Profile is a collection of mailbox settings.  Many people only have one Profile, but more than one can be created).

The most complete way to reset an account is to make a new Outlook Profile in Show Profiles from File | Info | Account Settings | Manage Profiles (or in Windows, Control Panel | Mail Setup | Profiles).  Making a new Outlook Profile is sometimes necessary to fix problems in the profile itself.

But making a new Profile is a right PITA especially if there’s multiple mailboxes.  So there’s a little shortcut that will probably work for a faulty OST fix.

Simply delete the mailbox connection within the existing Outlook profile.  Then add the account again.  Outlook will create a new OST file and download data according to the age setting.

Interim workarounds

All those suggestions are OK but not always practical.  If you’re ‘away’ using a slow or data limited connection, redownloading even some of your mailbox probably isn’t an option.

There are two workarounds to consider, these will keep you going until a better and unlimited data connection is available.

Turn Outlook Offline

Way off on the right of the Send/Receive tab is the Work Offline button.  Click that to stop all mailbox connections and use Outlook offline.

Use Outlook normally, read and write messages as usual.  Update Outlook by clicking ‘Work Offline’ again to go online for a few minutes.  Outlook will send any messages and receive new ones.  Go offline again.

That lets you continue working in Outlook but not leaving it always connected and gobbling up data.

Outlook in a browser

Another option is Outlook in your browser.  Use that instead or in tandem with Outlook desktop.

Metered Connections

If you’re not sure that Outlook is to blame for excessive data use, try Windows Metered Connections.  Any Internet connection can be marked as ‘Metered’ in Settings. It’s intended for internet links that charge for data or have a data limit.

Metered connections don’t download most Windows updates and Outlook will warn you before going online with a metered connection.

Thanks to the lovely Dr Jannicke for posing this interesting problem.

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