Problem in regex Email validator in C#

Question

I'm using the following code for validating email address which are present in an array. But after successfully validating first email address in an array, it is always returning false for next email address. May I know why it is behaving like that?

public static bool IsValidEmailID(string email)
        {
            string MatchEmailPattern =
            @"^(([\w-]+\.)+[\w-]+|([a-zA-Z]{1}|[\w-]{2,}))@"
     + @"((([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])\.([0-1]?
                [0-9]{1,2}|25[0-5]|2[0-4][0-9])\."
     + @"([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])\.([0-1]?
                [0-9]{1,2}|25[0-5]|2[0-4][0-9])){1}|"
     + @"([a-zA-Z]+[\w-]+\.)+[a-zA-Z]{2,4})$";

      Regex reStrict = new Regex(MatchEmailPattern);
            return reStrict.IsMatch(email);


        }

Update : The following code is getting email address from windows form text box:

String[] EmailArr = txtEmailID.Text.Split(new char[]{','},StringSplitOptions.RemoveEmptyEntries);

            for(int i = 0; i < EmailArr.Length; i++)
            {
               MessageBox.Show(IsValidEmailID(EmailArr[i])+" "+EmailArr[i]);
            }

Have you tried switching the position in the array of the first and second element, and see if it fails on the first one after the switch? — Øyvind Bråthen
– Øyvind Bråthen, Commented Mar 7, 2011 at 6:23
It is returning 'true' for the first element even after switching their position. — Joe
– Joe, Commented Mar 7, 2011 at 6:31
@Joe - Can you please post the code that calls the IsValidEmailID method also, and in addition the two first lines of the array? The problem is not with this code. I tried it on an array of valid e-mails, and it returned true for all of them. — Øyvind Bråthen
– Øyvind Bråthen, Commented Mar 7, 2011 at 6:41
@Joe, can you post your usage that is demonstrating the problem? — Jared Farrish
– Jared Farrish, Commented Mar 7, 2011 at 6:42
Does your txtEmailID.Text contain blanks/spaces? If so, trim the mail-addresses before checking them! — Philipp Grathwohl
– Philipp Grathwohl, Commented Mar 7, 2011 at 6:56

OrahSoft · Accepted Answer · 2011-03-07 07:04:25Z

This validation method works OK. I created an ArrayList and looping through array I'm calling your method to validate email. Here is sample loop:

bool result = false;
        ArrayList emails = new ArrayList();
        emails.Add("[email protected]");
        emails.Add("Hello.com");
        emails.Add("[email protected]");
        foreach (string email in emails)
        {
            result = IsValidEmailID(email);
        }

First time result equals to true, second to false and third to true. What kind of collection are you using? Maybe all emails except the first one are invalid....?

UPDATE:

I tested with your code

string textEmail = "[email protected],Hello.com,[email protected]";

        String[] EmailArr = textEmail.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries); 
        for (int i = 0; i < EmailArr.Length; i++) { Console.WriteLine(IsValidEmailID(EmailArr[i]) + " " + EmailArr[i]); }

Your split works well. The only think I may suggest is to trim string before validating. Textboxes sometimes have some extra spaces, which may cause issues.

IsVAludEmailID(EmailArr[i].Trim())

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