Theres many tools out there that will handle the follow up marketing part for you. Most will offer powerful workflow tools based on conditions etc.
Customers really appreciate it. I guess its not for everyone, and it's not infinitely scaleable but it is highly valuable in the early stages.
If you feel that a real human person is behind all that, and not a faceless company, you're also much more likely to share feedback. (Nobody would share improvement ideas for Windows with Microsoft, since you can be sure that those go straigth to /dev/null (or, more appropriately, the recycle bin).)
I get so much response when I email people. Every email is hand typed and I just say whatever comes to mind at the time.
Its super helpful for getting feedback and getting to know my customers.