[RESOLVED] Email address validation with RegEx

[MrGTI]

Hello.

I have been using a function to validate email addresses for awhile now. Yesterday i discovered that the code indicates that 2 different email addresses are invalid when in reality they are perfectly fine.

The code uses RegEx to determine if an email address is valid. I have tried to understand RegEx, but I can never seem to figure it out. Here is the code:

    Private Sub btnCheckEmail_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCheckEmail.Click
        If ValidateEmailAddress(txtEmail.Text) = True Then
            lblResult.Text = "Valid !"
        Else
            lblResult.Text = "X - BAD EMAIL - X"
        End If

        Beep()
    End Sub

    ''' <summary>
    ''' Use this function to check an email address to ensure it is in the proper format.
    ''' (It has an @ symbol, has a suffix to the domain name (ie: .com), does not contain any spaces, etc)
    ''' </summary>
    ''' <param name="sCheckEmailAddress">The email address to be checked.</param>
    ''' <returns>This function returns a boolean value. True is the email address is valid, False if it is not.</returns>
    Public Function ValidateEmailAddress(ByVal sCheckEmailAddress As String) As Boolean
        Try
            sCheckEmailAddress = Trim$(sCheckEmailAddress)
            Return Regex.IsMatch(sCheckEmailAddress, "^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$")
        Catch Exp As Exception
            Return False
        End Try
    End Function

Using that function, these 2 email addresses are flagged as being invalid:

[email protected]
[email protected]

How can the RegEx be re-written to allow the local part (before the @ symbol) to be 1 character, and/or be a number? I understand the "a-z" part, but i don't understand what [\w\.-] means, or why the a-z is duplicated before the @ symbol.
.

[ident]

Try

Option Strict On
 
Imports System.Text.RegularExpressions
 
Public Class MainForm
 
    Private Function ValidateEmailAddress(ByVal sCheckEmailAddress As String) As Boolean
        Return Regex.IsMatch(sCheckEmailAddress, "^([\w-]+\.)*?[\w-]+@[\w-]+\.([\w-]+\.)*?[\w]+$")
    End Function
 
    Private Sub btnCheckEmail_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCheckEmail.Click
        If ValidateEmailAddress(txtEmail.Text) Then
            lblResult.Text = "Valid !"
        Else
            lblResult.Text = "X - BAD EMAIL - X"
        End If
    End Sub
End Class

[MrGTI]

That works!

I still can't figure out the RegEx, but all the tests i ran came back valid when it should, and invalid when i entered bad email addresses.

Thank you.