I have used some javascript and Visual Basic and regular expressions to check for valid email addresses. It is going to be much more complex than you think, but there are some samples out there already.
Here is a JAVASCRIPT code:
// Email Validation Javascript
// copyright 23rd March 2003, by Stephen Chapman, Felgall Pty Ltd
// You have permission to copy and use this javascript provided that
// the content of the script is not changed in any way.
function validateEmail(addr,man,db) {
if (addr == '' && man) {
if (db) alert('email address is mandatory');
return false;
}
var invalidChars = '\/\'\\ ";:?!()[]\{\}^|';
for (i=0; i<invalidChars.length; i++) {
if (addr.indexOf(invalidChars.charAt(i),0) > -1) {
if (db) alert('email address contains invalid characters');
return false;
}
}
for (i=0; i<addr.length; i++) {
if (addr.charCodeAt(i)>127) {
if (db) alert("email address contains non ascii characters.");
return false;
}
}
var atPos = addr.indexOf('@',0);
if (atPos == -1) {
if (db) alert('email address must contain an @');
return false;
}
if (atPos == 0) {
if (db) alert('email address must not start with @');
return false;
}
if (addr.indexOf('@', atPos + 1) > - 1) {
if (db) alert('email address must contain only one @');
return false;
}
if (addr.indexOf('.', atPos) == -1) {
if (db) alert('email address must contain a period in the domain name');
return false;
}
if (addr.indexOf('@.',0) != -1) {
if (db) alert('period must not immediately follow @ in email address');
return false;
}
if (addr.indexOf('.@',0) != -1){
if (db) alert('period must not immediately precede @ in email address');
return false;
}
if (addr.indexOf('..',0) != -1) {
if (db) alert('two periods must not be adjacent in email address');
return false;
}
var suffix = addr.substring(addr.lastIndexOf('.')+1);
if (suffix.length != 2 && suffix != 'com' && suffix != 'net' && suffix != 'org' && suffix != 'edu' && suffix != 'int' && suffix != 'mil' && suffix != 'gov' & suffix != 'arpa' && suffix != 'biz' && suffix != 'aero' && suffix != 'name' && suffix != 'coop' && suffix != 'info' && suffix != 'pro' && suffix != 'museum') {
if (db) alert('invalid primary domain in email address');
return false;
}
return true;
}
Source is
http://javascript.about.com/od/completescripts/a/email.htm============================
Here is a Visual Basic version:
This validation example has been updated to reflect the possibility of up to 245 known ISO country codes in addition to the regular extensions of email addresses.
Option Explicit
Public EMsg As String 'used to return potential error messages in the functions below
Public Function ValidateEmail(ByVal strEmail As String) As Boolean
Dim strTmp As String, n As Long, sEXT As String
EMsg = "" 'reset on open for good form
ValidateEmail = True 'Assume true on init
sEXT = strEmail
Do While InStr(1, sEXT, ".") <> 0
sEXT = Right(sEXT, Len(sEXT) - InStr(1, sEXT, "."))
Loop
If strEmail = "" Then
ValidateEmail = False
EMsg = EMsg & "<BR>You did not enter an email address!"
ElseIf InStr(1, strEmail, "@") = 0 Then
ValidateEmail = False
EMsg = EMsg & "<BR>Your email address does not contain an @ sign."
ElseIf InStr(1, strEmail, "@") = 1 Then
ValidateEmail = False
EMsg = EMsg & "<BR>Your @ sign can not be the first character in your email address!"
ElseIf InStr(1, strEmail, "@") = Len(strEmail) Then
ValidateEmail = False
EMsg = EMsg & "<BR>Your @sign can not be the last character in your email address!"
ElseIf EXTisOK(sEXT) = False Then
ValidateEmail = False
EMsg = EMsg & "<BR>Your email address is not carrying a valid ending!"
EMsg = EMsg & "<BR>It must be one of the following..."
EMsg = EMsg & "<BR>.com, .net, .gov, .org, .edu, .biz, .tv Or included country's assigned country code"
ElseIf Len(strEmail) < 6 Then
ValidateEmail = False
EMsg = EMsg & "<BR>Your email address is shorter than 6 characters which is impossible."
End If
strTmp = strEmail
Do While InStr(1, strTmp, "@") <> 0
n = 1
strTmp = Right(strTmp, Len(strTmp) - InStr(1, strTmp, "@"))
Loop
If n > 1 Then
ValidateEmail = False 'found more than one @ sign
EMsg = EMsg & "<BR>You have more than 1 @ sign in your email address"
End If
End Function
Public Function EXTisOK(ByVal sEXT As String) As Boolean
Dim EXT As String, X As Long
EXTisOK = False
If Left(sEXT, 1) <> "." Then sEXT = "." & sEXT
sEXT = UCase(sEXT) 'just to avoid errors
EXT = EXT & ".COM.EDU.GOV.NET.BIZ.ORG.TV"
EXT = EXT & ".AF.AL.DZ.As.AD.AO.AI.AQ.AG.AP.AR.AM.AW.AU.AT.AZ.BS.BH.BD.BB.BY"
EXT = EXT & ".BE.BZ.BJ.BM.BT.BO.BA.BW.BV.BR.IO.BN.BG.BF.MM.BI.KH.CM.CA.CV.KY"
EXT = EXT & ".CF.TD.CL.CN.CX.CC.CO.KM.CG.CD.CK.CR.CI.HR.CU.CY.CZ.DK.DJ.DM.DO"
EXT = EXT & ".TP.EC.EG.SV.GQ.ER.EE.ET.FK.FO.FJ.FI.CS.SU.FR.FX.GF.PF.TF.GA.GM.GE.DE"
EXT = EXT & ".GH.GI.GB.GR.GL.GD.GP.GU.GT.GN.GW.GY.HT.HM.HN.HK.HU.IS.IN.ID.IR.IQ"
EXT = EXT & ".IE.IL.IT.JM.JP.JO.KZ.KE.KI.KW.KG.LA.LV.LB.LS.LR.LY.LI.LT.LU.MO.MK.MG"
EXT = EXT & ".MW.MY.MV.ML.MT.MH.MQ.MR.MU.YT.MX.FM.MD.MC.MN.MS.MA.MZ.NA"
EXT = EXT & ".NR.NP.NL.AN.NT.NC.NZ.NI.NE.NG.NU.NF.KP.MP.NO.OM.PK.PW.PA.PG.PY"
EXT = EXT & ".PE.PH.PN.PL.PT.PR.QA.RE.RO.RU.RW.GS.SH.KN.LC.PM.ST.VC.SM.SA.SN.SC"
EXT = EXT & ".SL.SG.SK.SI.SB.SO.ZA.KR.ES.LK.SD.SR.SJ.SZ.SE.CH.SY.TJ.TW.TZ.TH.TG.TK"
EXT = EXT & ".TO.TT.TN.TR.TM.TC.TV.UG.UA.AE.UK.US.UY.UM.UZ.VU.VA.VE.VN.VG.VI"
EXT = EXT & ".WF.WS.EH.YE.YU.ZR.ZM.ZW"
EXT = UCase(EXT) 'just to avoid errors
If InStr(1, sEXT, EXT, vbBinaryCompare) <> 0 Then EXTisOK = True
End Function
Source is
http://www.developerfusion.com/show/3350/====================================
And a third version that uses REGULAR EXPRESSIONS:
<script language="vbscript">
function ValidateEmail(sEmail)
set myExpression = new RegExp
myExpression.pattern = "^(\w+\.)*(\w+)@(\w+\.)+([a-zA-Z]{2,4})$"
If myExpression.test(sEmail.value) = True Then
msgbox "Valid Email"
Else
msgbox "Invalid Email"
End If
End Function
</script>
Source is
http://www.devx.com/tips/Tip/15306===================================
These can at least give you an idea of some of the approaches that others have taken.
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