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POBest Regular Expression for Email Format Validation with ASP.NET 3.5 Validation
 

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  1. POBest Regular Expression for Email Format Validation with ASP.NET 3.5 Validation
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    <p>I've used both of the following Regular Expressions for testing for a valid email expression with ASP.NET validation controls. I was wondering which is the better expression from a performance standpoint, or if someone has better one.</p> <pre> - \w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)* - ^([0-9a-zA-Z]([-\.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$ </pre> <p>I'm trying avoid the "exponentially slow expression" problem described on the <a href="http://blogs.msdn.com/b/bclteam/archive/2005/02/10/370690.aspx" rel="noreferrer">BCL Team Blog</a>.</p> <p><strong>UPDATE</strong></p> <p>Based on feedback I ended up creating a function to test if an email is valid:</p> <pre><code>Public Function IsValidEmail(ByVal emailString As String, Optional ByVal isRequired As Boolean = False) As Boolean Dim emailSplit As String() Dim isValid As Boolean = True Dim localPart As String = String.Empty Dim domainPart As String = String.Empty Dim domainSplit As String() Dim tld As String If emailString.Length &gt;= 80 Then isValid = False ElseIf emailString.Length &gt; 0 And emailString.Length &lt; 6 Then 'Email is too short isValid = False ElseIf emailString.Length &gt; 0 Then 'Email is optional, only test value if provided emailSplit = emailString.Split(CChar("@")) If emailSplit.Count &lt;&gt; 2 Then 'Only 1 @ should exist isValid = False Else localPart = emailSplit(0) domainPart = emailSplit(1) End If If isValid = False OrElse domainPart.Contains(".") = False Then 'Needs at least 1 period after @ isValid = False Else 'Test Local-Part Length and Characters If localPart.Length &gt; 64 OrElse ValidateString(localPart, ValidateTests.EmailLocalPartSafeChars) = False OrElse _ localPart.StartsWith(".") OrElse localPart.EndsWith(".") OrElse localPart.Contains("..") Then isValid = False End If 'Validate Domain Name Portion of email address If isValid = False OrElse _ ValidateString(domainPart, ValidateTests.HostNameChars) = False OrElse _ domainPart.StartsWith("-") OrElse domainPart.StartsWith(".") OrElse domainPart.Contains("..") Then isValid = False Else domainSplit = domainPart.Split(CChar(".")) tld = domainSplit(UBound(domainSplit)) ' Top Level Domains must be at least two characters If tld.Length &lt; 2 Then isValid = False End If End If End If Else 'If no value is passed review if required If isRequired = True Then isValid = False Else isValid = True End If End If Return isValid End Function </code></pre> <p>Notes: </p> <ul> <li>IsValidEmail is more restrictive about characters allowed then the RFC, but it doesn't test for all possible invalid uses of those characters</li> </ul>
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