We have recently migrated our exchange users from a 2010 exchange to 2013 exchange. 

Users have Outlook 2010 and recently some of these users have been having issues when sending emails. The emails will sit in the Outbox and not send. 

We currently have cached exchange mode enabled (would prefer to keep this enabled.) 

Currently the resolution for this issue is to recreate the users profile which obviously recreates the OST file on the local PC (this fixes the problem) unfortunately this isn't a good work around when there's 20000 users... 

does anyone know of a fix for this?

Hello,

If you are having problem with Microsoft Outlook 2010 through exchange server and using cached mode you should try these steps overcome with this issue.  

1.  Close MS Outlook.
2.   Press Window Key+ R  to open run dialog box >> Type regedit  & click OK
3. Check if you have this registry key: HKCU\Software\Microsoft\Office\12.0\Outlook\Cached Mode

If not, then create that key.

Add a new DWORD value inside, name it Send One.

Set the value to 0.

Thanks & Regards

Clark Kent

• Edited by Clark445Kent 2 hours 28 minutes ago