It would be great to have this section, where you have a starting point (for example, send the first mail),

then you have intermediate steps.. like see if the lead opens the email or answer it.. if they answer the email, then send the second email, if not, send the first email again.. etc.

And finally, you have the final step (like adding a task to the user if the lead didn't complete all the steps and add a label to the leads that completed all steps).

Last, have some reports about how it did go...