Is there is a way to see what email clients our leads are using? Ideally, we want to see the percentages of the email clients being used but we'd be fine with having this information at any level. I did find this page (Email Client Market Share and Popularity - July 2015) and we want to see if our database lines up with those results.
You can setup a system using Smart Lists:
Email Clicks (or Open) with the Device constraint. I recommend using a list of possible options because it will be very long for individual Devices, so I group them by Android, iOS, etc.
This will be directional only, it will not be 100% perfect.
It has always bugged me that this is not a standard report - considering that Marketo is an email/mobile first company and tool! However there are ways you can get to this info and it involved smart lists. You can also do what others suggest, and what I reocmmend is to integrate Litmus.