Instead of just sending your users emails based on time (i.e., X days after signup), figure out how far along the activation flow they should be—and then change the email based on whether or not they’re on track or off track. If they should have knocked out two of their stepping stones by day 7, and they haven’t done it yet, you should be sending them a customized email to help get them unblocked (and ideally having a CS person reach out as well).
