What is the step by step process of publishing APK file using Email?
How do you define "publish"? You can certainly send someone a .apk by email:
But that's not "publishing" it such that anyone that you didn't email it to can access it...
To expand on what @jonp said, there are something things that owners of the device must do to allow that APK to be installed : explicitly allow applications that are not from Google Play to be installed.
Part 5 - Publishing Independently of the Publishing an Application guide contains some details on this.
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