Due to viruses Microsoft decided to block certain types of attachments,
better, decided to block certain filename extentions. This is a rather
clueless idea, because noone[1] would ban blue cars, if one blue car
caused an accident[2]... but its Microsoft.
The blocked extentions are common ones like .exe, .hlp or .cmd.
If you send mails with those filetypes as an attachment you get
a warning. And the receiver only sees the
(paper clip) but can't access the file.
Disruptor OL can grant access to the blocked files per item or auto-export
the files.
To protect the innocent, the 'secure' option allows to change the
extention to a double-click-save one.