Rinat Abdullin

Here's another one:

static readonly Regex _emailRegex = new Regex(
  @"^[a-z0-9](([_\.\-\'\+]?[a-z0-9]+)*)" +
  @"@(([a-z0-9]{1,64})(([\.\-][a-z0-9]{1,64})*)\.([a-z]{2,})" +
  @"|(\d{1,3}(\.\d{1,3}){3}))$",
  RegexOptions.Compiled | RegexOptions.Singleline 
    | RegexOptions.IgnoreCase);

This RegEx accepts these proper emails:

• l3tt3rsAndNumb3rs@domain.com
• has-dash@domain.com
• hasApostrophe.o'leary@domain.org
• uncommonTLD@domain.museum
• uncommonTLD@domain.travel
• uncommonTLD@domain.mobi
• countryCodeTLD@domain.uk
• lettersInDomain@911.com
• underscore_inLocal@domain.net
• IPInsteadOfDomain@127.0.0.1
• subdomain@sub.domain.com
• local@dash-inDomain.com
• dot.inLocal@foo.com
• a@singleLetterLocal.org
• singleLetterDomain@x.org
• disposable+email@gmail.com

And these invalid emails are rejected:

• two@@signs.com
• missingDomain@.com
• @missingLocal.org
• missingatSign.net
• missingDot@com
• colonButNoPort@127.0.0.1:
• [Empty]
• someone-else@127.0.0.1.26
• .localStartsWithDot@domain.com
• localEndsWithDot.@domain.com
• two..consecutiveDots@domain.com
• domainStartsWithDash@-domain.com
• domainEndsWithDash@domain-.com
• numbersInTLD@domain.c0m
• missingTLD@domain.
• ! ""#$%(),/;[]`|@invalidCharsInLocal.org
• invalidCharsInDomain@! ""#$%(),/;<>_[]`|.org
• local@SecondLevelDomainNamesAreInvalidIfTheyAreLongerThan64Charactersss.org

If you are using Lokad Shared Libraries, then you can reference this email validation rule directly in your enforce statements like:

Enforce.Argument(email, "email", StringRules.ValidEmail);

or build more complex and reusable validation rules:

Enforce.Argument(account, "account", ValidAccount);

// ...
public static void ValidAccount(Account account, IScope scope)
{
  scope.Validate(account.Username, "Username", 
    StringRules.Limit(6, 256), 
    StringRules.ValidEmail);

  scope.Validate(account.Password, "Password", 
    StringRules.Limit(1, 256));
}

Update on Monday, November 17, 2008 at 12:17 by Rinat Abdullin

Tweaked the regex to support disposable emails in format of 'disposable+email@gmail.com'. Unit tests in the Shared Libraries were also updated.