Hi Joe,
FormMule (FM) created a couple of columns, and one of those contains the send status (=reply from the mailserver).
Look for in row 1 of your FormResponse-tab for the header 'Template 1 - Send Status' (or your more specific template name).
Now, for every cell in this column where LEN()>0 you will probably see the reply or error of the server.
However, if you put something in the cells of the Send Status column(s) yourself (like: 'Completed: request processed')
you will prevent FM the hard way not to sent any mails for this old record for this specific template.
However, the more elegant approach is come up with some clear conditions which much be met before you allow FM to sent anything at all.
Add another column to be labeled as 'Template 1 - Send Condition'
As requests older than say three weeks - which should therefor not be mailed about anymore - you could setup an ARRAYFORMULA() to automate the calculation to match the condition for each record:
=ARRAYFORMULA( IF( ROW(A:A)=1, "Template 1 - Send Condition', IF( LEN(A:A)=0, "",
...and from there you test the amount of DAYS(A:A) for the record...
IF( DAYS(A:A) > 21, FALSE, DAYS(A:A) )
or something like that...
...and use the column as the conditional for the specific template in FM.
And yes, if you can think of more conditions to 'harden' your solution...
...create more columns with a test to the records to which the requrement has to meet.
I hope this make some sense to you ;)
Cheers, Bart