Check email in Vb.net desktop application

Imports System.Text.RegularExpressions

Public Function IsEmail(ByVal str As String) As Boolean

If (str = Nothing) Then
Return False
ElseIf (str = "") Then
Return False
Else
Dim pattern As String = "^[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]$"
Dim emailAddressMatch As Match = Regex.Match(str, pattern)

If emailAddressMatch.Success Then
Return True
Else
Return False
End If
End If

End Function