Thank you Alistair - I hadn't thought of that at all and it must be the reason why when I set the campaign up as mentioned above - recipients receive the mailer twice. I've set my wait up for 2 days. Is that enough?
I had another support ticket open that touched on this topic too and I think maybe the support technician clarified this for me even further. I'm going to copy his response here for you:
query from me: I have used the flow if mail soft bounces, wait a couple days and then send again. My recipients though indicated they received the mailers more than once....Is this solely because I had not restricted them to run through the program once only? Is there a specific time I should incorporate as a "wait" to ensure the system isn't still trying to mail to them when my next mail goes out?
response from support (seems the wait wasn't the issue - although I was using a 2 day wait): You'll want to change the "Default Choice" to a blank item. Meaning, if it soft bounced, send the email again. It it didn't, don't send anything because the 1st email made it through and was delivered.
** I had not left the default field blank, so my recipients were receiving multiple messages from me.