Answer
This situation may occur when an antivirus like Norton Antivirus is installed on the same machine as GFI LANguard. By default Norton Antivirus has enabled the email scanning options. In this case Norton Antivirus will respond to requests done to ports 25 and 110 and GFI LANguard will report the ports as being open on all the machines that are scanned.
To avoid the problem you should disable 'Scan incoming Email' and 'Scan outgoing Email' options in Norton Antivirus.
This issue may also occur with other antivirus products and with certain firewall configurations.