These settings belong to the Attachment Filter.
The Attachment Filter blocks mails that contain suspicious attachments. By default, it looks for executable files with the following extensions:
.com, .scr, .pif, .bat, .exe, .vbs, .bas, .cmd, .cpl, .lnk, .reg, .vb, .vbe, .wsh
You can add new extensions by clicking on the “Add” button.
Of course, you can remove certain items from the list, too. Just click on them and press the “Delete” button.