Outlook 2016 user's email not updating while on cached mode - 0365

Hello all,

A few months ago our firm migrated from Exchange 2010 to 0365. We have one user whose emails did not automatically update while on cache mode after the initial migration but after a bit of messing around (recreating profile, changing some DNS entry's etc..) it was syncing again. She mentioned this issue started up again yesterday morning although we have not made any changes. The email sends/receive while on non cached mode but outlook tends to operate slow on non cache so its not an option for us.

This is whats been done at the moment:
Ran a repair on 2013 when it was installed
Deleted & recreated a new outlook profile
Deleted existing ost files
Ran CCleaner
Upgraded from 2013 to 2016 to further test if it was software related since we've had some weird issues with 2013
Issue persisted on 2016, deleting everything again and am currently re-downloading the ost while on cache mode. The initial Download of the ost works its after the first download where it does not sync/update emails. Sending works fine however.

Additional info:
The user is using office 2016
Windows 7 64bit
LAN connection on a lenovo thinkpad W540
Windows environment, HP switches & Sophos firewalls.
No other users experience this issue while on cache mode. At most we have search problems on some users which on cache.

Unfortunately this is for a higher up user in the company and I've been on this for a bit and can't figure it out. Thanks for help in advance! This is my first time posting a question here so please let me know if i've left out any additional data you may need.


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MacleanSystem EngineerCommented:
I would suggest to log on with another profile, setup email, and see if the same issue occurs.
If not, then re-create the users windows profile (I know its a pain, but it often works)
But if it still occurs on the other profileI would try to run the full Office uninstall tool from Microsoft.
Just in case run the 2013 version as well.
Tom CieslikIT EngineerCommented:
Check size of initial ost file. Maybe there is a restriction on file since maybe original outlook was older one like 2007 or older and was upgraded over the years.
Microsoft do not recommend to have OST files bigger than 20GB, but if you have to you can change limit in Registry

Maximum .OST file size in Unicode is 20GB for Outlook 2007 and 50GB for Outlook 2010/2013/2016. By default the maximum size is set to 20GB. When the .OST file reaches or exceeds this limit, you will encounter one or more of the following errors:

Cannot open or load the OST file at all.
Cannot add any new data to the OST file.
Cannot synchronize the OST file with the Exchange server.
Various error messages during the synchronization process.

You may modify the following UNICODE Registry values to increase the limits:

The MaxLargeFileSize registry entry. The MaxFileSize registry entry determines the absolute maximum size that both the .pst and the .ost files can grow to. After this maximum size is reached, Outlook does not permit the size of the file to grow beyond this size.
The WarnLargeFileSize registry entry. The WarnFileSize registry entry determines the maximum data that both the .pst and the .ost files can have. After this maximum data is reached, neither the .pst nor the .ost files are permitted to add any more data. However, the size of the physical file may still increase because of internal processes.

To proceed follow the steps below:

Open Registry: Start > in Search field type in "regedit" without quotes.
Navigate to
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\PST for Outlook 2007,
HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\PST for Outlook 2010,
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\PST for Outlook 2013,
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST for Outlook 2016.
Right-click on MaxLargeFileSize in the right pane > Modify > type in value in MB in Value Data box > Ok.
Right-click on WarnLargeFileSize in the right pane > Modify > type in value in MB in Value Data box > Ok.


In the following table, the MaxLargeFileSize registry entry and the WarnLargeFileSize registry entry refer to a UNICODE formatted (new Large format) file, and the MaxFileSize registry entry and the WarnFileSize registry entry refer to an ANSI formatted (an earlier Microsoft Outlook format) file. The UNICODE values are set in megabyte (MB) increments, while the ANSI values are set in byte increments.
Outlook 2016, 2013, and 2010

Name                           Type                              Valid Data Range                             Default
MaxLargeFileSize            REG_DWORD      0x00000001 – 0x0000C800      0x0000C800 51,200 (50 GB)
WarnLargeFileSize      REG_DWORD      0x00000000 – 0x0000BE00      0x0000BE00 48,640 (47.5 GB)
MaxFileSize                     REG_DWORD      0x001F4400 – 0x7C004400      0x7BB04400 2,075,149,312 (1.933 GB)
WarnFileSize                     REG_DWORD      0x00042400 – 0x7C004400      0x74404400 1,950,368,768 (1.816 GB)

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Tom CieslikIT EngineerCommented:
Best solution provided, no more other questions from author
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