How to use regex to match an email address in C#

Regex rules for email address validation

Pattern	Explanation
`[a-z]`	The regex pattern `[a-z]` matches any lowercase letter from "a" to "z". It can be used to check if a string contains a lowercase letter.
`[A-Z]`	The regex pattern `[A-Z]` matches any uppercase letter from "A" to "Z". It can be used to check if a string contains an uppercase letter.
`[0-9]`	`[0-9]` represents a character class that matches any single digit from 0 to 9. It can be used to search for or match any digit character in a string.
`^`	`^` asserts the start of the string. It indicates that the following pattern should match from the beginning of the string.
`+`	When a plus sign (`+`) appears after a regular expression in a regular expression pattern, it is used as a quantifier. It indicates that the preceding regular expression should match one or more occurrences.

Here's a breakdown of how the regular expression works:

^ asserts the start of the string.
[a-zA-Z0-9.!#$%&'*+-/=?^_{|}~]+` matches one or more characters from the set of alphabets (lowercase and uppercase), digits, and special characters that are allowed in the local part of an email address.
@ matches the "@" symbol.
[a-zA-Z0-9-]+ matches one or more characters from the set of alphabets (lowercase and uppercase), digits, and hyphens that are allowed in the domain name part of an email address.
(?:\.[a-zA-Z0-9-]+)* is a non-capturing group that matches zero or more occurrences of a dot followed by one or more characters from the set of alphabets (lowercase and uppercase), digits, and hyphens. This allows for multiple domain levels, such as "example.com" or "subdomain.example.com".
$ asserts the end of the string.

Overall, this regular expression can be used to validate that a given string represents a valid email address.

Let's now look at a coding example to match an email address.

Coding example

using System;
using System.Text.RegularExpressions;
public class Program
{
    public static void Main()
    {
        string[] email_addrs = { "test@example.com", "user@example@com", "invalid_email" };
        foreach (string i in email_addrs)
        {
            bool is_Valid_Email = ValidateEmail(i);
            if (is_Valid_Email)
            {
                Console.WriteLine($"{i} is a valid email address.");
            }
            else
            {
                Console.WriteLine($"{i} is an invalid email address.");
            }
        }
    }
    public static bool ValidateEmail(string Email_Address)
    {
        string reg_pattern = @"^[a-zA-Z0-9.!#$%&'*+-/=?^_`{|}~]+@[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$";
        Regex regex = new Regex(reg_pattern);
        return regex.IsMatch(Email_Address);
    }
}

Explanation

Lines 6–23: In the function Main, we define an array of email addresses (email_addrs) that need to be validated. The program then iterates over each email address in the array and calls the ValidateEmail function to check if it is valid.
Lines 25–32: The ValidateEmail function takes an email address as input and returns a boolean value indicating whether the email address is valid or not. It utilizes a regular expression pattern to perform the validation. The function creates a Regex object with the pattern and uses the IsMatch method to check if the email address matches the pattern.

The program outputs a message indicating whether each email address is valid or invalid based on the validation result.

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Free Resources

How to use regex to match an email address in C#

Regex rules for email address validation

Regular expression

Coding example

Explanation