How To Use Outlook With a Mailbox Larger Than 50GB

Updated 17 November 20251 min read4 steps

If your Mweb mailbox is larger than 50GB, Outlook may not sync all your mail because of a built-in file size limit. You can safely increase this limit in Windows to keep using Outlook without losing mail.

1. Check Your Outlook Version

   These steps apply to Outlook 2010, 2013, 2016, 2019, and Microsoft 365 for Windows.
   If you’re using Outlook 2007 or earlier, please upgrade before continuing.

2. Increase the Outlook Data File Size Limit

   Outlook stores your emails in a local data file (PST or OST). By default, the limit is 50GB. To raise it:

   1. Close Outlook.

   2. Press Windows key + R, type regedit, and press Enter.

   3. Go to:

      HKEY_CURRENT_USER\Software\Microsoft\Office\<version>\Outlook\PST

      Replace <version> with:

      • Outlook 2016, 2019, 365 = 16.0

      • Outlook 2013 = 15.0

      • Outlook 2010 = 14.0

   4. Right-click PST, select New > DWORD (32-bit) Value.

   5. Name it MaxLargeFileSize and set the value (in MB):

      • Example: 102400 = 100 GB

   6. Create another DWORD named WarnLargeFileSize and set it slightly lower (e.g. 95000 = 95 GB).

   7. Close the Registry Editor and reopen Outlook.

3. Keep Performance in Mind

   • Outlook may slow down if your data file grows beyond 100GB.

   • Archive old mail into a separate PST file.

   • Use folders and rules to manage large inboxes.

   • Turn on Cached Exchange Mode for smoother performance.

4. Use Webmail for Very Large Mailboxes

   For mailboxes exceeding 100GB, you can access your email directly at https://www.mweb.co.za/webmail. Webmail connects straight to our servers and is not limited by Outlook’s local file size restrictions.