I've Installed F-Secure Email and Server Security but Windows Defender Real-time Protection is still on. Should I deactivate it when I'm using the F-Secure product?
Yes, Windows Defender should be deactivated when using F-Secure Email and Server Security. Multiple Anti-Virus products running at the same time may cause conflicts.
On Windows Server 2016/2019, Windows Defender will not enter passive or disabled mode if you install a third-party antivirus.
After installing a third-party antivirus you should uninstall Windows Defender AV on Windows Server 2016 to prevent problems caused by having multiple antivirus products installed on a machine.
If you are Using Windows Server, version 1803 and Windows 2019, you can enable passive mode by setting this registry key:
Path: HKLM\SOFTWARE\Policies\Microsoft\Windows Advanced Threat Protection
Article no: 000002236