Why do the Android 5.0 and Android 6.0 previews in Litmus differ from what I see on my phone?
In Android 5 (Lollipop), Google decoupled their native apps (alarm clock, calendar, email, etc) from their OS, making it possible for vendors to use the Android OS without being forced to integrate the default apps, too. Now, these apps are available as open source to vendors (like Litmus—or Samsung, who make phones) and the public. Vendors can use the “vanilla” version of the email app, make any changes they like, or develop their very own email app from scratch and make it available to their users.
Because of this, the Android marketplace sees a great deal of fragmentation, and all device manufacturers have full control over how they implement the email app. The rendering for the "email" app on Android devices can differ from device to device—and from what you see on Litmus. Litmus previews represent the “vanilla” Android email app, and this is one single type of Android email app preview out of hundreds. As newer versions of Android do not have the default mail app installed, Litmus will not support newer versions of the default mail app because the market share for those is effectively non-existent.
There are many variables that may impact Android email rendering: Gmail vs. "email" app, brand/device manufacturer, Gmail vs. IMAP account, screen size, etc. Litmus offers several variations and you can see the full list here. While the heavy fragmentation makes it nearly impossible to provide coverage for all possible variations, we’re always working on providing the most popular ones in Litmus.