How to validate email address inputs?

Question

I have an ASP.NET web form where I can can enter an email address.

I need to validate that field with acceptable email addresses ONLY in the below pattern:

xxx@home.co.uk
xxx@home.com
xxx@homegroup.com

Answer 1

A regular expression to validate this would be:

^[A-Z0-9._%+-]+((@home\.co\.uk)|(@home\.com)|(@homegroup\.com))$

C# sample:

string emailAddress = "jim@home.com";
string pattern = @"^[A-Z0-9._%+-]+((@home\.co\.uk)|(@home\.com)|(@homegroup\.com))$";
if (Regex.IsMatch(emailAddress, pattern, RegexOptions.IgnoreCase))
{
    // email address is valid
}

VB sample:

Dim emailAddress As String = "jim@home.com"
Dim pattern As String = "^[A-Z0-9._%+-]+((@home\.co\.uk)|(@home\.com)|(@homegroup\.com))$";
If Regex.IsMatch(emailAddress, pattern, RegexOptions.IgnoreCase) Then
    ' email address is valid
End If

Answer 2

Here's how I would do the validation using System.Net.Mail.MailAddress:

bool valid = true;
try
{
    MailAddress address = new MailAddress(email);
}
catch(FormatException)
{
    valid = false;
}

if(!(email.EndsWith("@home.co.uk") || 
     email.EndsWith("@home.com") || 
     email.EndsWith("@homegroup.com")))
{
    valid = false;
}

return valid;

MailAddress first validates that it is a valid email address. Then the rest validates that it ends with the destinations you require. To me, this is simpler for everyone to understand than some clumsy-looking regex. It may not be as performant as a regex would be, but it doesn't sound like you're validating a bunch of them in a loop ... just one at a time on a web page

Answer 3

Depending on what version of ASP.NET your are using you can use one of the Form Validation controls in your toolbox under 'Validation.' This is probably preferable to setting up your own logic after a postback. There are several types that you can drag to your form and associate with controls, and you can customize the error messages and positioning as well.

There are several types that can make it a required field or make sure its within a certain range, but you probably want the Regular Expression validator. You can use one of the expressions already shown or I think Visual Studio might supply a sample email address one.

Answer 4

You could use a regular expression.

See e.g. here:

http://tim.oreilly.com/pub/a/oreilly/windows/news/csharp_0101.html

Answer 5

I second the use of a regex, however Patrick's regex won't work (wrong alternation). Try:

[A-Z0-9._%+-]+@home(\.co\.uk|(group)?\.com)

And don't forget to escape backslashes in a string that you use in source code, depending on the language used.

"[A-Z0-9._%+-]+@home(\\.co\\.uk|(group)?\\.com)"

Answer 6

Here is the official regex from RFC 2822, which will match any proper email address:

(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])

Answer 7

Try this:

Regex matcher = new Regex(@"([a-zA-Z0-9_\-\.]+)\@((home\.co\.uk)|(home\.com)|(homegroup\.com))");

if(matcher.IsMatch(theEmailAddressToCheck))
{
    //Allow it
}
else
{
    //Don't allow it
}

You'll need to add the Regex namespace to your class too:

using System.Text.RegularExpressions;

Answer 8

An extension method to do this would be:

public static bool ValidEmail(this string email)
    {
        var emailregex = new Regex(@"[A-Za-z0-9._%-]+(@home\.co\.uk$)|(@home\.com$)|(@homegroup\.com$)");
        var match = emailregex.Match(email);
        return match.Success;
    }

Answer 9

Use a <asp:RegularExpressionValidator ../> with the regular expression in the ValidateExpression property.

Answer 10

Patricks' answer seems pretty well worked out but has a few flaws.

• You do want to group parts of the regex but don't want to capture them. Therefore you'll need to use non-capturing parenthesis.
• The alternation is partly wrong.
• It does not test if this was part of the string or the entire string
• It uses Regex.Match instead of Regex.IsMatch.

A better solution in C# would be:

string emailAddress = "someone@home.co.uk";
if (Regex.IsMatch(emailAddress, @"^[A-Z0-9._%+-]+@home(?:\.co\.uk|(?:group)?\.com)$", RegexOptions.IgnoreCase))
{
    // email address is valid
}

Of course to be completely sure that all email addresses pass you can use a more thorough expression:

string emailAddress = "someone@home.co.uk";
if (Regex.IsMatch(emailAddress, @"^[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@home(?:\.co\.uk|(?:group)?\.com)$", RegexOptions.IgnoreCase))
{
    // email address is valid
}