Avoiding insertion of a redundant suffix to recipient's Email

Running Outlook 2007, an Expert has assisted me in coding a script which appends a suffix to the recipient's Email address.  For details, please see https://www.experts-exchange.com/questions/28374041/Automatically-appending-a-suffix-to-Email-recipient's-address.html

This works just as I had hoped, but there is a small, unexpected issue.  I have Outlook configured to suspend "sent" messages in the Outbox until a second instance of Send/Receive is executed.  Sometimes I need to review an outbound message, before sending it, and this approach allows me to do that.  If I open a message in the Outbox, make any changes, and then send it, the script appends a second suffix to the recipient's Email address.  If I'm paying attention, of course I will delete the redundant suffix.  However, if there's an easy way to adjust the script so that another suffix won't be added, I'd like to know.