对@齿轮回答做了一点修改

public static bool IsValidEmail(this string email)
{
  // skip the exception & return early if possible
  if (email.IndexOf("@") <= 0) return false;

  try
  {
    var address = new MailAddress(email);
    return address.Address == email;
  }
  catch
  {
    return false;
  }
}

我根据维基百科的规则和样本地址创建了一个电子邮件地址验证程序。对于那些不介意多看一点代码的人，这里。说实话，我不知道电子邮件地址规范中有这么多疯狂的规则。我没有完全验证主机名或ipaddress，但它仍然通过了维基百科上的所有测试用例。

using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace EmailValidateUnitTests
{
    [TestClass]
    public class EmailValidationUnitTests
    {
        [TestMethod]
        public void TestEmailValidate()
        {
            // Positive Assertions
            Assert.IsTrue("prettyandsimple@example.com".IsValidEmailAddress());
            Assert.IsTrue("very.common@example.com".IsValidEmailAddress());
            Assert.IsTrue("disposable.style.email.with+symbol@example.com".IsValidEmailAddress());
            Assert.IsTrue("other.email-with-dash@example.com".IsValidEmailAddress());
            Assert.IsTrue("\"much.more unusual\"@example.com".IsValidEmailAddress());
            Assert.IsTrue("\"very.unusual.@.unusual.com\"@example.com".IsValidEmailAddress()); //"very.unusual.@.unusual.com"@example.com
            Assert.IsTrue("\"very.(),:;<>[]\\\".VERY.\\\"very@\\\\ \\\"very\\\".unusual\"@strange.example.com".IsValidEmailAddress()); //"very.(),:;<>[]\".VERY.\"very@\\ \"very\".unusual"@strange.example.com
            Assert.IsTrue("admin@mailserver1".IsValidEmailAddress());
            Assert.IsTrue("#!$%&'*+-/=?^_`{}|~@example.org".IsValidEmailAddress());
            Assert.IsTrue("\"()<>[]:,;@\\\\\\\"!#$%&'*+-/=?^_`{}| ~.a\"@example.org".IsValidEmailAddress()); //"()<>[]:,;@\\\"!#$%&'*+-/=?^_`{}| ~.a"@example.org
            Assert.IsTrue("\" \"@example.org".IsValidEmailAddress()); //" "@example.org (space between the quotes)
            Assert.IsTrue("example@localhost".IsValidEmailAddress());
            Assert.IsTrue("example@s.solutions".IsValidEmailAddress());
            Assert.IsTrue("user@com".IsValidEmailAddress());
            Assert.IsTrue("user@localserver".IsValidEmailAddress());
            Assert.IsTrue("user@[IPv6:2001:db8::1]".IsValidEmailAddress());
            Assert.IsTrue("user@[192.168.2.1]".IsValidEmailAddress());
            Assert.IsTrue("(comment and stuff)joe@gmail.com".IsValidEmailAddress());
            Assert.IsTrue("joe(comment and stuff)@gmail.com".IsValidEmailAddress());
            Assert.IsTrue("joe@(comment and stuff)gmail.com".IsValidEmailAddress());
            Assert.IsTrue("joe@gmail.com(comment and stuff)".IsValidEmailAddress());

            // Failure Assertions
            Assert.IsFalse("joe(fail me)smith@gmail.com".IsValidEmailAddress());
            Assert.IsFalse("joesmith@gma(fail me)il.com".IsValidEmailAddress());
            Assert.IsFalse("joe@gmail.com(comment and stuff".IsValidEmailAddress());
            Assert.IsFalse("Abc.example.com".IsValidEmailAddress());
            Assert.IsFalse("A@b@c@example.com".IsValidEmailAddress());
            Assert.IsFalse("a\"b(c)d,e:f;g<h>i[j\\k]l@example.com".IsValidEmailAddress()); //a"b(c)d,e:f;g<h>i[j\k]l@example.com
            Assert.IsFalse("just\"not\"right@example.com".IsValidEmailAddress()); //just"not"right@example.com
            Assert.IsFalse("this is\"not\\allowed@example.com".IsValidEmailAddress()); //this is"not\allowed@example.com
            Assert.IsFalse("this\\ still\\\"not\\\\allowed@example.com".IsValidEmailAddress());//this\ still\"not\\allowed@example.com
            Assert.IsFalse("john..doe@example.com".IsValidEmailAddress());
            Assert.IsFalse("john.doe@example..com".IsValidEmailAddress());
            Assert.IsFalse(" joe@gmail.com".IsValidEmailAddress());
            Assert.IsFalse("joe@gmail.com ".IsValidEmailAddress());
        }
    }

    public static class ExtensionMethods
    {
        private const string ValidLocalPartChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!#$%&'*+-/=?^_`{|}~";
        private const string ValidQuotedLocalPartChars = "(),:;<>@[]. ";
        private const string ValidDomainPartChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-:";

        private enum EmailParseMode
        {
            BeginLocal, Local, QuotedLocalEscape, QuotedLocal, QuotedLocalEnd, LocalSplit, LocalComment,
            At,
            Domain, DomainSplit, DomainComment, BracketedDomain, BracketedDomainEnd
        };

        public static bool IsValidEmailAddress(this string s)
        {
            bool valid = true;

            bool hasLocal = false, hasDomain = false;
            int commentStart = -1, commentEnd = -1;
            var mode = EmailParseMode.BeginLocal;
            for (int i = 0; i < s.Length; i++)
            {
                char c = s[i];
                if (mode == EmailParseMode.BeginLocal || mode == EmailParseMode.LocalSplit)
                {
                    if (c == '(') { mode = EmailParseMode.LocalComment; commentStart = i; commentEnd = -1; }
                    else if (c == '"') { mode = EmailParseMode.QuotedLocal; }
                    else if (ValidLocalPartChars.IndexOf(c) >= 0) { mode = EmailParseMode.Local; hasLocal = true; }
                    else { valid = false; break; }
                }
                else if (mode == EmailParseMode.LocalComment)
                {
                    if (c == ')')
                    {
                        mode = EmailParseMode.Local; commentEnd = i;
                        // comments can only be at beginning and end of parts...
                        if (commentStart != 0 && ((commentEnd + 1) < s.Length) && s[commentEnd + 1] != '@') { valid = false; break; }
                    }
                }
                else if (mode == EmailParseMode.Local)
                {
                    if (c == '.') mode = EmailParseMode.LocalSplit;
                    else if (c == '@') mode = EmailParseMode.At;
                    else if (c == '(') { mode = EmailParseMode.LocalComment; commentStart = i; commentEnd = -1; }
                    else if (ValidLocalPartChars.IndexOf(c) >= 0) { hasLocal = true; }
                    else { valid = false; break; }
                }
                else if (mode == EmailParseMode.QuotedLocal)
                {
                    if (c == '"') { mode = EmailParseMode.QuotedLocalEnd; }
                    else if (c == '\\') { mode = EmailParseMode.QuotedLocalEscape; }
                    else if (ValidLocalPartChars.IndexOf(c) >= 0 || ValidQuotedLocalPartChars.IndexOf(c) >= 0) { hasLocal = true; }
                    else { valid = false; break; }
                }
                else if (mode == EmailParseMode.QuotedLocalEscape)
                {
                    if (c == '"' || c == '\\') { mode = EmailParseMode.QuotedLocal; hasLocal = true; }
                    else { valid = false; break; }
                }
                else if (mode == EmailParseMode.QuotedLocalEnd)
                {
                    if (c == '.') { mode = EmailParseMode.LocalSplit; }
                    else if (c == '@') mode = EmailParseMode.At;
                    else if (c == '(') { mode = EmailParseMode.LocalComment; commentStart = i; commentEnd = -1; }
                    else { valid = false; break; }
                }
                else if (mode == EmailParseMode.At)
                {
                    if (c == '[') { mode = EmailParseMode.BracketedDomain; }
                    else if (c == '(') { mode = EmailParseMode.DomainComment; commentStart = i; commentEnd = -1; }
                    else if (ValidDomainPartChars.IndexOf(c) >= 0) { mode = EmailParseMode.Domain; hasDomain = true; }
                    else { valid = false; break; }
                }
                else if (mode == EmailParseMode.DomainComment)
                {
                    if (c == ')')
                    {
                        mode = EmailParseMode.Domain;
                        commentEnd = i;
                        // comments can only be at beginning and end of parts...
                        if ((commentEnd + 1) != s.Length && (commentStart > 0) && s[commentStart - 1] != '@') { valid = false; break; }
                    }
                }
                else if (mode == EmailParseMode.DomainSplit)
                {
                    if (ValidDomainPartChars.IndexOf(c) >= 0) { mode = EmailParseMode.Domain; hasDomain = true; }
                    else { valid = false; break; }
                }
                else if (mode == EmailParseMode.Domain)
                {
                    if (c == '(') { mode = EmailParseMode.DomainComment; commentStart = i; commentEnd = -1; }
                    else if (c == '.') { mode = EmailParseMode.DomainSplit; }
                    else if (ValidDomainPartChars.IndexOf(c) >= 0) { hasDomain = true; }
                    else { valid = false; break; }
                }
                else if (mode == EmailParseMode.BracketedDomain)
                {
                    if (c == ']') { mode = EmailParseMode.BracketedDomainEnd; }
                    else if (c == '.' || ValidDomainPartChars.IndexOf(c) >= 0) { hasDomain = true; }
                    else { valid = false; break; }
                }
                else if (mode == EmailParseMode.BracketedDomain)
                {
                    if (c == '(') { mode = EmailParseMode.DomainComment; commentStart = i; commentEnd = -1; }
                    else { valid = false; break; }
                }
            }
            bool unfinishedComment = (commentEnd == -1 && commentStart >= 0);

            return hasLocal && hasDomain && valid && !unfinishedComment;
        }
    }
}

如果你真的，我是说真的想知道一个电子邮件地址是否有效……请邮件交换器来证明它，不需要正则表达式。如果需要，我可以提供代码。

一般步骤如下: 1. 电子邮件地址有域名部分吗?(@ > 0的索引) 2. 使用DNS查询询问域是否有邮件交换器 3.打开到邮件交换器的TCP连接 4. 使用SMTP协议，以电子邮件地址作为接收者打开到服务器的消息 5. 解析服务器的响应。 6. 如果你能走到这一步，就别发短信了，一切都好。

正如您可以想象的那样，这是非常昂贵的时间，并且依赖于smtp，但它确实有效。

There are a lot of strong answers here. However, I recommend that we take a step back. @Cogwheel answers the question https://stackoverflow.com/a/1374644/388267. Nevertheless, it could be costly in a bulk validation scenario, if many of the email address being validated are invalid. I suggest that we employ a bit of logic before we enter into his try-catch block. I know that the following code could be written using RegEx but that could be costly for new developers to understand. This is my twopence worth:

    public static bool IsEmail(this string input)
    {
        if (string.IsNullOrWhiteSpace(input)) return false;

        // MUST CONTAIN ONE AND ONLY ONE @
        var atCount = input.Count(c => c == '@');
        if (atCount != 1) return false;

        // MUST CONTAIN PERIOD
        if (!input.Contains(".")) return false;

        // @ MUST OCCUR BEFORE LAST PERIOD
        var indexOfAt = input.IndexOf("@", StringComparison.Ordinal);
        var lastIndexOfPeriod = input.LastIndexOf(".", StringComparison.Ordinal);
        var atBeforeLastPeriod = lastIndexOfPeriod > indexOfAt;
        if (!atBeforeLastPeriod) return false;

        // CODE FROM COGWHEEL'S ANSWER: https://stackoverflow.com/a/1374644/388267 
        try
        {
            var addr = new System.Net.Mail.MailAddress(input);
            return addr.Address == input;
        }
        catch
        {
            return false;
        }
    }

我从第1条中得到Phil的答案，并创建了这个类。 这样调用它:bool isValid = Validator.EmailIsValid(emailString);

下面是这个类:

using System.Text.RegularExpressions;

public static class Validator
{

    static Regex ValidEmailRegex = CreateValidEmailRegex();

    /// <summary>
    /// Taken from http://haacked.com/archive/2007/08/21/i-knew-how-to-validate-an-email-address-until-i.aspx
    /// </summary>
    /// <returns></returns>
    private static Regex CreateValidEmailRegex()
    {
        string validEmailPattern = @"^(?!\.)(""([^""\r\\]|\\[""\r\\])*""|"
            + @"([-a-z0-9!#$%&'*+/=?^_`{|}~]|(?<!\.)\.)*)(?<!\.)"
            + @"@[a-z0-9][\w\.-]*[a-z0-9]\.[a-z][a-z\.]*[a-z]$";

        return new Regex(validEmailPattern, RegexOptions.IgnoreCase);
    }

    internal static bool EmailIsValid(string emailAddress)
    {
        bool isValid = ValidEmailRegex.IsMatch(emailAddress);

        return isValid;
    }
}

正如在许多回答中提到的，电子邮件地址的领域是复杂的。在这种情况下，我强烈反对使用正则表达式。那些匹配(大多数)用例的异常复杂，难以读取，因此也难以维护。此外，它们仍然难以支持所有病例，而且速度缓慢。

微软的EmailAddress类在这方面有所帮助，但我认为也不是完美的。在几年前的一个开源项目中，我尝试使用定制的EmailParser。

在[EmailAddress]https://github.com/Qowaiv/Qowaiv/blob/master/src/Qowaiv/EmailAddress.cs中使用。

通过使用这种方法，不仅可以验证电子邮件地址，还可以清除显示名称的多种格式，去掉mailto:-前缀，并根据ip地址规范化域字面量，并将所有内容小写(注意，本地部分是大小写敏感的)。

你的解决方案应该支持的场景(上面提到的就是):

[TestCase(null)]
[TestCase("")]
[TestCase("..@test.com")]
[TestCase(".a@test.com")]
[TestCase("ab@sd@dd")]
[TestCase(".@s.dd")]
[TestCase("ab@988.120.150.10")]
[TestCase("ab@120.256.256.120")]
[TestCase("ab@120.25.1111.120")]
[TestCase("ab@[188.120.150.10")]
[TestCase("ab@188.120.150.10]")]
[TestCase("ab@[188.120.150.10].com")]
[TestCase("a@b.-de.cc")]
[TestCase("a@bde-.cc")]
[TestCase("a@bde.c-c")]
[TestCase("a@bde.cc.")]
[TestCase("ab@b+de.cc")]
[TestCase("a..b@bde.cc")]
[TestCase("_@bde.cc,")]
[TestCase("plainaddress")]
[TestCase("plain.address")]
[TestCase("@%^%#$@#$@#.com")]
[TestCase("@domain.com")]
[TestCase("Joe Smith <email@domain.com>")]
[TestCase("email.domain.com")]
[TestCase("email@domain@domain.com")]
[TestCase(".email@domain.com")]
[TestCase("email.@domain.com")]
[TestCase("email..email@domain.com")]
[TestCase("email@-domain.com")]
[TestCase("email@domain-.com")]
[TestCase("email@domain.com-")]
[TestCase("email@.domain.com")]
[TestCase("email@domain.com.")]
[TestCase("email@domain..com")]
[TestCase("email@111.222.333")]
[TestCase("email@111.222.333.256")]
[TestCase("email@[123.123.123.123")]
[TestCase("email@[123.123.123].123")]
[TestCase("email@123.123.123.123]")]
[TestCase("email@123.123.[123.123]")]
[TestCase("email@{leftbracket.com")]
[TestCase("email@rightbracket}.com")]
[TestCase("email@p|pe.com")]
[TestCase("isis@100%.nl")]
[TestCase("email@dollar$.com")]
[TestCase("email@r&d.com")]
[TestCase("email@#hash.com")]
[TestCase("email@wave~tilde.com")]
[TestCase("email@exclamation!mark.com")]
[TestCase("email@question?mark.com")]
[TestCase("email@obelix*asterisk.com")]
[TestCase("email@grave`accent.com")]
[TestCase("email@colon:colon.com")]
[TestCase("email@caret^xor.com")]
[TestCase("email@=qowaiv.com")]
[TestCase("email@plus+.com")]
[TestCase("email@domain.com>")]
[TestCase("email( (nested) )@plus.com")]
[TestCase("email)mirror(@plus.com")]
[TestCase("email@plus.com (not closed comment")]
[TestCase("email(with @ in comment)plus.com")]
[TestCase(@"""Joe Smith email@domain.com")]
[TestCase(@"""Joe Smith' email@domain.com")]
[TestCase(@"""Joe Smith""email@domain.com")]
[TestCase("email@mailto:domain.com")]
[TestCase("mailto:mailto:email@domain.com")]
[TestCase("Display Name <email@plus.com> (after name with display)")]
[TestCase("ReDoSaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")]
public void IsInvalid(string email)
{
    Assert.IsFalse(EmailAddress.IsValid(email), email);
}

[TestCase("w@com")]
[TestCase("w.b.f@test.com")]
[TestCase("w.b.f@test.museum")]
[TestCase("a.a@test.com")]
[TestCase("ab@288.120.150.10.com")]
[TestCase("ab@188.120.150.10")]
[TestCase("ab@1.0.0.10")]
[TestCase("ab@120.25.254.120")]
[TestCase("ab@01.120.150.1")]
[TestCase("ab@88.120.150.021")]
[TestCase("ab@88.120.150.01")]
[TestCase("ab@[120.254.254.120]")]
[TestCase("local@2001:0db8:85a3:0000:0000:8a2e:0370:7334")]
[TestCase("local@[2001:0db8:85a3:0000:0000:8a2e:0370:7334]")]
[TestCase("2@bde.cc")]
[TestCase("-@bde.cc")]
[TestCase("a2@bde.cc")]
[TestCase("a-b@bde.cc")]
[TestCase("ab@b-de.cc")]
[TestCase("a+b@bde.cc")]
[TestCase("f.f.f@bde.cc")]
[TestCase("ab_c@bde.cc")]
[TestCase("_-_@bde.cc")]
[TestCase("k.haak@12move.nl")]
[TestCase("K.HAAK@12MOVE.NL")]
[TestCase("email@domain.com")]
[TestCase("email@domain")]
[TestCase("あいうえお@domain.com")]
[TestCase("local@あいうえお.com")]
[TestCase("firstname.lastname@domain.com")]
[TestCase("email@subdomain.domain.com")]
[TestCase("firstname+lastname@domain.com")]
[TestCase("email@123.123.123.123")]
[TestCase("email@[123.123.123.123]")]
[TestCase("1234567890@domain.com")]
[TestCase("a@domain.com")]
[TestCase("a.b.c.d@domain.com")]
[TestCase("aap.123.noot.mies@domain.com")]
[TestCase("1@domain.com")]
[TestCase("email@domain-one.com")]
[TestCase("_______@domain.com")]
[TestCase("email@domain.topleveldomain")]
[TestCase("email@domain.co.jp")]
[TestCase("firstname-lastname@domain.com")]
[TestCase("firstname-lastname@d.com")]
[TestCase("FIRSTNAME-LASTNAME@d--n.com")]
[TestCase("first-name-last-name@d-a-n.com")]
[TestCase("{local{name{{with{@leftbracket.com")]
[TestCase("}local}name}}with{@rightbracket.com")]
[TestCase("|local||name|with|@pipe.com")]
[TestCase("%local%%name%with%@percentage.com")]
[TestCase("$local$$name$with$@dollar.com")]
[TestCase("&local&&name&with&$@amp.com")]
[TestCase("#local##name#with#@hash.com")]
[TestCase("~local~~name~with~@tilde.com")]
[TestCase("!local!!name!with!@exclamation.com")]
[TestCase("?local??name?with?@question.com")]
[TestCase("*local**name*with*@asterisk.com")]
[TestCase("`local``name`with`@grave-accent.com")]
[TestCase("^local^^name^with^@xor.com")]
[TestCase("=local==name=with=@equality.com")]
[TestCase("+local++name+with+@equality.com")]
[TestCase("Joe Smith <email@domain.com>")]
[TestCase("email@domain.com (joe Smith)")]
[TestCase(@"""Joe Smith"" email@domain.com")]
[TestCase(@"""Joe\\tSmith"" email@domain.com")]
[TestCase(@"""Joe\""Smith"" email@domain.com")]
[TestCase(@"Test |<gaaf <email@domain.com>")]
[TestCase("MailTo:casesensitve@domain.com")]
[TestCase("mailto:email@domain.com")]
[TestCase("Joe Smith <mailto:email@domain.com>")]
[TestCase("Joe Smith <mailto:email(with comment)@domain.com>")]
[TestCase(@"""With extra < within quotes"" Display Name<email@domain.com>")]
[TestCase("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")]
public void IsValid(string email)
{
    Assert.IsTrue(EmailAddress.IsValid(email), email);
}