1. You have to download and extract Office 2010 Administration templates to be able to edit Office GPO. You download it fromt he below link. Download the one that suits your system.
http://www.microsoft.com/en-us/download/details.aspx?id=18968
2. You need also to down Simple MAPI GPO configuration from the below link.
http://download.microsoft.com/download/6/D/1/6D113C3D-4651-4DE3-A501-7B602B0E0DEC/Outlk14-simplemapi.adm
3. Open GPM. Create a GPO and link it to the required OU. Edit the GPO.
4. Open User Configuration / Polcies. Right click on Adminitrative templates. Add / Remove templates.
5. Go to your extracted (ADM folder)/downloaded files and choose outlk14 and outlk14-simplemapi
6. Now these templates been added to your administrative templates.
7. Go to User Configuration\Policies\Administrative Templates\Classic Administrative Templates (ADM)\Security\Security Form Settings.
8. Enable Outlook Security Mode and choose Use Outlook Security Group Policy.
9. Go to User Configuration\Policies\Administrative Templates\Classic Administrative Templates (ADM)\Security\Security Form Settings\Programmatic Security. Enable the following GPOs.
And setup each GPO to "Automatically approved"
10. Login with a users and test that the following registery keys have the following value.
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Outlook\Security
Dword: PromptOOMSend
Value: 2
Dword: PromptOOMAddressBookAccess
value: 2
Dword : PromptOOMAddressInformationAccess
Value:2
Dword: PromptOOMMeetingTaskRequestResponse
Value: 2
Dword: PromptOOMSaveAs
Value: 2
Dword: PromptOOMFormulaAccess
Value: 2
Dword: PromptSimpleMAPISend
Value: 2
Dword: PromptSimpleMAPINameResolve
Value: 2
Dword: PromptSimpleMAPIOpenMessage
Value : 2
Now users will be able to send emails without any problems.