Clarify EmailId

[alankley]

What is a valid email id?
I'm unable to use valid dynamic gmail addresses with special characters (+, .)

We should distinguish "correct" email address (what user provided) and correctly FORMED email addresses.
If incorrectly formed we should display what format we expect as an error message

I recommend we refer to the email always as an email. I don't recommend we use it as an ID to identify a user in the database. The user might want to change their email. We CAN allow them to use it to login. Optionally we can offer a username. A username can be used in the UI to identify a user on the map, etc.

The ID of the user item in the database can be duplicated inside the User item and used as a unique key/id. It can serve as the key in Maps for convenient retrieval.

[alankley]

On Android, there is the following Pattern:
public static final Pattern EMAIL_ADDRESS
= Pattern.compile(
"[a-zA-Z0-9\+\.\_\%\-\+]{1,256}" +
"\@" +
"[a-zA-Z0-9][a-zA-Z0-9\-]{0,64}" +
"(" +
"\." +
"[a-zA-Z0-9][a-zA-Z0-9\-]{0,25}" +
")+"
);

Valid Email on Android can be checked with:
android.util.Patterns.EMAIL_ADDRESS.matcher(targetEmail).matches()