Eventually you could then add more pro tracking features such as average time to respond.

average time to respond - I would definitely pay for that additional feature

14hr30 min average time to respond for day for brand1

20hour 20 min average time for month for brand1

23hrs 00 or week average time for brand1

4 days 23hours Longest respond time for brand1

4 days 23hours Longest respond time for brand1

You could have similar time tracking features than mailmeter has for gmail based on a time range. I would definitely pay $15 a month more for timetracking feature for my mail app. You should have tiers perhaps. 15 email addresses, 25 addresses , 50 addresses etc.

Could be similar to what email meter does for gmail.