We use google apps for work, and we want to be able to track our users gmail activities, like how many emails they receive, how many emails they reply & fail to reply.>
If you're just looking for email counts, I would use the Gmail API to do this (I use that currently for the same). You will not get email logs though, in case you're looking for details on potential delays / rejections /etc. I do not believe there is a Reports API section geared for this at the moment.