If you are using an email service such as Constant Contact or MailChimp, they offer fantastic statistical reports on how many people are opening your messages, what device they are using, etc. I want to alert you that a recent software change may cause an unexpected "bump" in your statistics.
Gmail just a made a change to automatically open images in messages. The way email services track "opens" is by burying a tiny, one-pixel image in the email. When the message is opened, if images are downloaded, the act of fetching the embedded image records that message as being opened.
iPhones automatically download images. Gmail did not; as a default setting, you had to ask Gmail to fetch the images in a message. So a message sent to an Android phone would require an extra action by the user to register as an open, as compared to iPhones. As a result, iPhones were over-represented in statistics of which devices were used by people reading your emails. Google obviously has an incentive to combat that perception, so they changed Gmail software so that it works like iPhones in this regard.
It will now be just as easy for an Android user to show as having opened your email. The net result is that you should begin to see a bump in your open rates, and this bump will come from Android users whose phones and tablets will now automatically download images. Be ready to account for it as you look at your email stats in the coming weeks.