What version of FileMaker Pro are you using?
Can you use the option to send the emails directly to the SMTP server?
I am having the same issue. I'm using FileMaker Pro 8.5 and I do not have the option of sending directly to the SMTP server as we are a large organization with Outlook on an Exchange server.
I finally spent the time to get a script automated and to now have to click allow for each email defeats the purpose.