Binaryworld - IsValidEmail - Validate an email address ... [ VB.net -> Regular Expression ]

Function IsValidEmail(ByVal Value As String, Optional ByVal MaxLength As _
  Integer = 255, Optional ByVal IsRequired As Boolean = True) As Boolean
  If Value Is Nothing OrElse Value.Length = 0 Then
    ' rule out the null string case
    Return Not IsRequired
  ElseIf Value.Length > MaxLength Then
    ' rule out values that are longer than allowed
    Return False
  End If

  ' search invalid chars
  If Not System.Text.RegularExpressions.Regex.IsMatch(Value, _
    "^[-A-Za-z0-9_@.]+$") Then Return False

  ' search the @ char
  Dim i As Integer = Value.IndexOf("@"c)
  ' there must be at least three chars after the @
  If i <= 0 Or i >= Value.Length - 3 Then Return False
  ' ensure there is only one @ char
  If Value.IndexOf("@"c, i + 1) >= 0 Then Return False

  ' check that the domain portion contains at least one dot
  Dim j As Integer = Value.LastIndexOf("."c)
  ' it can't be before or immediately after the @ char
  If j < 0 Or j <= i + 1 Then Return False

  ' if we get here the address if validated
  Return True
End Function