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TIP: Validate an E-Mail Address

  • September 19, 2002
  • By Karl Moore
  • Send Email »
  • More Articles »

Need to ensure an e-mail address is valid?

This copy-and-paste code snippet checks an address for its length, the @ sign, the period, the characters used, the suffix - and more!

Save your overworked fingers further strain and add this snippet to your code library.

To use it, simply call the IsEMailAddress function, passing in an e-mail address and an optional 'reason' string variable. The procedure will return a True if the e-mail address is valid, a False otherwise.

If False is returned, the reason for its failure will be passed back into the optional reason string.

With thanks to Paul Brown for the code base (slightly revised for publication).

Usage

Dim IsValid As Boolean
Dim InvalidReason As String
    
IsValid = IsEMailAddress("karl@karlmoore.com", _ 
                         InvalidReason)

MsgBox "Is the e-mail address valid? - " & IsValid

MsgBox "If invalid, the reason given is: " & InvalidReason

Code

Public Function IsEMailAddress(ByVal sEmail As String, _
    Optional ByRef sReason As String) As Boolean
        
	Dim sPreffix As String
	Dim sSuffix As String
	Dim sMiddle As String
	Dim nCharacter As Integer
	Dim sBuffer As String

	sEmail = Trim(sEmail)

	If Len(sEmail) < 8 Then
		IsEMailAddress = False
		sReason = "Too short"
		Exit Function
	End If


	If InStr(sEmail, "@") = 0 Then
		IsEMailAddress = False
		sReason = "Missing the @"
		Exit Function
	End If


	If InStr(InStr(sEmail, "@") + 1, sEmail, "@") <> 0 Then
		IsEMailAddress = False
		sReason = "Too many @"
		Exit Function
	End If


	If InStr(sEmail, ".") = 0 Then
		IsEMailAddress = False
		sReason = "Missing the period"
		Exit Function
	End If

	If InStr(sEmail, "@") = 1 Or InStr(sEmail, "@") = Len(sEmail) Or _
		InStr(sEmail, ".") = 1 Or InStr(sEmail, ".") = Len(sEmail) Then
		IsEMailAddress = False
		sReason = "Invalid format"
	Exit Function

End If


For nCharacter = 1 To Len(sEmail)
	sBuffer = Mid$(sEmail, nCharacter, 1)
	If Not (LCase(sBuffer) Like "[a-z]" Or sBuffer = "@" Or _
	sBuffer = "." Or sBuffer = "-" Or sBuffer = "_" Or _
	IsNumeric(sBuffer)) Then: IsEMailAddress = _
	False: sReason = "Invalid character": Exit Function
Next nCharacter

nCharacter = 0

On Error Resume Next

sBuffer = Right(sEmail, 4)
If InStr(sBuffer, ".") = 0 Then GoTo TooLong:
If Left(sBuffer, 1) = "." Then sBuffer = Right(sBuffer, 3)
If Left(Right(sBuffer, 3), 1) = "." Then sBuffer = Right(sBuffer, 2)
If Left(Right(sBuffer, 2), 1) = "." Then sBuffer = Right(sBuffer, 1)


If Len(sBuffer) < 2 Then
	IsEMailAddress = False
	sReason = "Suffix too short"
	Exit Function
End If

TooLong:

If Len(sBuffer) > 3 Then
	IsEMailAddress = False
	sReason = "Suffix too long"
	Exit Function
End If

sReason = Empty
IsEMailAddress = True

End Function





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