Delete them:
HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\{KEY2KEY2KEY2}
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\S-1-5-18\Products\KEYKEYKEY
HKCR\Installer\Products\KEYKEYKEY
HKLM\SOFTWARE\Wow6432Node\SOMETHING
HKLM\SOFTWARE\RegisteredApplications\SOMETHING
HKLM\SOFTWARE\Clients\Mail\SOMETHINGifITdidHANDLEmail
HKLM\SOFTWARE\WOW6432Node\RegisteredApplications\SOMETHING
HKU\.DEFAULT\Software\Clients\Mail\SOMETHINGifITwasAmailCLIENT
HKU\S-1-5-18\Software\Clients\Mail\SOMETHINGifITwasAmailCLIENT