See a breakdown of first open and first clicks by device via Email > Reporting > Device Reporting
The breakdown shows stats on which device was used the first time a Recipient Opened and Clicked the email.
There are times where Maxemail will not be given the complete details from the email client to determine exactly which device the engagement happened on.
Examples of this would include Gmail webmail & mobile apps and Outlook.com where a proxy is used to retrieve the images.
In these cases, rather than skew the stats unfairly in favour of one of the other devices, they are simply recorded as Unknown.