How do I measure the length of my mail in pixels?
The easiest option to measure this is by the length of the mail on the screen. What you can fit onto one screen when the iPad is in portrait mode is approximately 1000 pixels, if you scroll down, each screen (page) length adds another 1000 pixels. Although the ideal length for newsletters is around 1500 pixels, your device will probably be fine generating mails up to 2500 pixels or more.