I don’t think that conditional formatting is the way, if I were in your shoes I’d rather search for VBA code that is triggered on a value change in the given cell.
For column W use this: IF(Z=””,”UNSENT”,”SENT”)
You could try this in column W:
that will put the word SENT in the column W if there is something entered in column Z
but if nothing exists in column Z then it would put your formula in from earlier
Hope that helps