When Matching Users Via Email, Changing Email Address Does Not Change Login

Question

Well, the subject pretty much says it all, but here're some examples of what's going on:
Initial Data
- Create 2 Business Partners in SAP, C1 and C2.
- Create 2 Contact Employees in SAP, Adam with email adam at eden.org in C1 and Eve with no email in C2.
Synch
- Run Initial Synch followed by Standard Synch (for good measure).
- Web Tools gets user Adam with username adam at eden.org.
- Web Tools gets user Eve with username 2, the unique key for SAP's Contact Employee.
Data Change In SAP
- Adam's email is removed.
- Eve's email is populated with eve at eden.org.
Resynch
- Run Standard Synch.
- Web Tools changes both email addresses, with Adam's being erased and Eve's becoming eve at eden.org.
- Web Tools does not change the UserID, leaving Adam's as adam at eden.org and Eve's as 2.
That last bullet is the big problem: if a user changes an email address, the username doesn't change. Is there any way to change this across the board, or perhaps even force users to login via their current email address?

Answer 1

Also, there is a field in the Users table called EmailLogin. I have tried without success to change this field so that the user would use this field to login instead of the UserID, but have been unsuccessful in getting it to work.
As an alternative, the login control in /plugins/loginblock.ascx contains, as a portion, the following code:
    protected void loginMain_LoggedIn(object sender, EventArgs e) {
        NPUser user = new NPUser(loginMain.UserName);
        ((NPBasePage)Page).Login(user.UserID, user.AccountID, false);
Wouldn't it be simple to do the following?
    protected void GetUserIDFromDBByEmail(string email) {
        string userid;
        System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection();
        System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand(conn, "SELECT Users.UserID FROM Users WHERE Users.Email='" + email.Replace("'", "''") + "'");
        userid = (string)cmd.ExecuteScalar();
        cmd.Connection.Close();
        conn.Close();
    protected void loginMain_LoggedIn(object sender, EventArgs e) {
        string userid;
        // Though we're passing the "username" from the form,
        // we know that we're expecting the email to be in it
        userid = GetUserIDFromDBByEmail(loginMain.UserName);
        NPUser user = new NPUser(userid);
        ((NPBasePage)Page).Login(user.UserID, user.AccountID, false);
Again, the benefit to this is that you can synch using the Internal B1 Contact Code, which will remain constant and unique, and have the availability to change the way the user logs in by modifying the email address. Of course, email addresses would have to remain unique as well, but that's an easy enough thing to check for.