/// <summary>
/// Robust e-mail validation (takes into account ip address and valid characters)
/// </summary>
/// <param name="emailAddress">E-Mail Address to check</param>
/// <returns>Blank if E-mail Address is valid, Error message if not.</returns>
public static string ValidEmail(string emailAddress)
{
string errorMessage;
try
{
if (emailAddress.Length == 0)
{
errorMessage = "E-Mail Address Is Blank";
return(errorMessage);
}
/* The following variable tells the rest of the function whether or not
* to verify that the address ends in a two-letter country or well-known
* TLD. 1 means check it, 0 means don't. */
const int checkTLD = 1;
/* The following is the list of known TLDs that an e-mail address must end with. */
string knownDomsPat = "^(com|net|org|edu|int|mil|gov|arpa|biz|aero|name|coop|info|pro|museum)$";
/* The following pattern is used to check if the entered e-mail address
* fits the user@domain format. It also is used to separate the username
* from the domain. */
Regex emailPat = new Regex("^([^@]+)@([^@]+)$");
/* The following string represents the pattern for matching all special
* characters. We don't want to allow special characters in the address.
* These characters include ( ) < > @ , ; : \ " . [ ] */
//string specialChars="\\(\\)><@,;:\\\\\\\"\\.\\[\\]";
string specialChars = @"\(\)<>@,;:\\\.\[\]\" + StringUtil.Chr(34);
/* The following string represents the range of characters allowed in a
* username or domainname. It really states which chars aren't allowed.*/
//string validChars=@"\[^\\s" + specialChars + @"\]";
string validChars = @"[^\s" + specialChars + "]";
/* The following pattern applies if the "user" is a quoted string (in
* which case, there are no rules about which characters are allowed
* and which aren't; anything goes). E.g. "jiminy cricket"@disney.com
* is a legal e-mail address. */
//string quotedUser="******"[^\"]*\")";
string quotedUser = "******" + StringUtil.Chr(34) + "[^\\" + StringUtil.Chr(34) + "]*\\" + StringUtil.Chr(34) + ")";
/* The following pattern applies for domains that are IP addresses,
* rather than symbolic names. E.g. joe@[123.124.233.4] is a legal
* e-mail address. NOTE: The square brackets are required. */
string ipDomainPat = @"^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$";
/* The following string represents an atom (basically a series of non-special characters.) */
string atom = validChars + '+';
/* The following string represents one word in the typical username.
* For example, in [email protected], john and doe are words.
* Basically, a word is either an atom or quoted string. */
string word = "(" + atom + "|" + quotedUser + ")";
// The following pattern describes the structure of the user
Regex userPat = new Regex("^" + word + "(\\." + word + ")*$");
/* The following pattern describes the structure of a normal symbolic
* domain, as opposed to ipDomainPat, shown above. */
Regex domainPat = new Regex("^" + atom + "(\\." + atom + ")*$");
/* Finally, let's start trying to figure out if the supplied address is valid. */
/* Begin with the coarse pattern to simply break up user@domain into
* different pieces that are easy to analyze. */
Match myMatch;
myMatch = emailPat.Match(emailAddress);
//Original
//var matchArray=emailStr.match(emailPat);
if (myMatch.Groups.Count != 3)
{
/* Too many/few @'s or something; basically, this address doesn't
* even fit the general mould of a valid e-mail address. */
errorMessage = "Email address is incorrect (check @ and .'s)";
return(errorMessage);
}
string user = myMatch.Groups[1].Value;
string domain = myMatch.Groups[2].Value;
// Start by checking that only basic ASCII characters are in the strings (0-127).
for (int i = 0; i < user.Length; i++)
{
if (StringUtil.Asc(user.Substring(i, 1)) > 127)
{
errorMessage = "E-mail user name contains invalid characters.";
return(errorMessage);
}
}
for (int i = 0; i < domain.Length; i++)
{
if (StringUtil.Asc(domain.Substring(i, 1)) > 127)
{
errorMessage = "The E-mail domain name contains invalid characters.";
return(errorMessage);
}
}
// See if "user" is valid
if (userPat.IsMatch(user) == false)
{
// user is not valid
errorMessage = "The E-mail username is not valid.";
return(errorMessage);
}
/* if the e-mail address is at an IP address (as opposed to a symbolic
* host name) make sure the IP address is valid. */
Match IPMatch;
IPMatch = Regex.Match(domain, ipDomainPat);
if (IPMatch.Groups.Count > 1)
{
// this is an IP address
for (int i = 1; i <= 4; i++)
{
if (Convert.ToInt16(IPMatch.Groups[i].Value) > 255)
{
errorMessage = "E-Mail Destination IP address is invalid";
return(errorMessage);
}
}
return("");
}
// Domain is symbolic name. Check if it's valid.
if (domainPat.IsMatch(domain) == false)
{
errorMessage = "E-mail domain name is not valid.";
return(errorMessage);
}
int len = StringUtil.NumberOfWords(domain, ".");
/* domain name seems valid, but now make sure that it ends in a
* known top-level domain (like com, edu, gov) or a two-letter word,
* representing country (uk, nl), and that there's a hostname preceding
* the domain or country. */
if (checkTLD == 1 && StringUtil.GetField(domain, len, ".").Length != 2 &&
!Regex.IsMatch(StringUtil.GetField(domain, len, "."), knownDomsPat))
{
errorMessage = "The E-Mail address must end in a well-known domain or two letter " + "country.";
return(errorMessage);
}
// If we've gotten this far, everything's valid!
return("");
}
catch (Exception ex)
{
return("Error in E-Mail Validation routine: " + ex.Message);
}
}