https://checkup.frontapp.com allows to scan a Gmail inbox to get some basic activity metrics.
I see the number of sent emails over the last 100 days is totally underestimated if I compare with https://mail.google.com/mail/u/0/#sent/. How does Frontapp's count the number of sent emails?
Using the request
from:(firstname.lastname@example.org) after:2014/8/22 before:2014/10/23, I see I sent emails in 420 different threads over the last 30 months, which is more than Frontapp's checkup count of number of sent emails: