PGP Desktop continues prompting for your passphrase for each email message, regardless if the email is encrypted or not. This occurs if you try to open any email from a recipient for which you have a public key in PGP Desktop.
This is caused when Microsoft Outlook 2010 Add-In "People Pane" is enabled. "People Pane" connects all information related to person in Outlook.
This issue is resolved by deactivating the "People Pane" Add-In in Microsoft Outlook 2010.
Use the following steps:
1. Go to "View" in Microsoft Outlook
2. Click on the icon "People Pane"
3. Deactivate the Add-In.