I would guess that your email client program is not permitting FileMaker to use it to send an email.... You may need to change a setting in your email client to permit this.
That was my assumption also. I couldnt find anything to allow Outlook 2013 to send. I checked the settings against a Windows XP machine and they are identical. The only variable is Windows XP and Outlook 2010. I am wondering if it has somethign to do with UAC settings?
I figured it out. It was McAfee 8.8. By default it blocks programs from sending out what McAfee considers "mass email" I just added the .exe file to the program exception list, tested and the emails are flowing.