I was undertaking a communication exercise. Ran into this one niggle for which I ended up writing up a quick script.
Problem: Had sent one round of emails. When the next set of emails got picked up, had to ensure that the ones to which mails were sent already, those emails were removed.
Solution: The following GScript helped me resolve. It checks for each email from the sent emails list and marks Mailed / Not Mailed against each. Added in a line to have duplicates removed as well in the process.
Improvements: In the next iteration, wish to have the the mail also go to those emails that gets identified as Not Mailed by picking up from the drafts and have the entry moved to the sent sheet itself.
Impact: Jo was about to get this done manually. The script + workflow design easily saves countless hours of mindless work. Not to mention the elimination of human error and fatigue that comes with such tasks.