foreach (KeyValuePair<string, string> kvp in accounts)
            {
                if(kvp.Key.Contains("gmail"))
                {
//mail....
                 }

other way:

Dictionary<string, string> emails = new Dictionary<string, string>();

foreach (string combo in File.ReadAllLines(@"C:\User\Comp\Desktop\file.txt"))
{
    string[] values = combo.Split(':');
    if (values.Length >= 2)
    {
        // Filter here... for example...
        if (values[0].Containsh("gmail"))
        {
            // Now your emails will only be added if they match your criteria...
            emails.Add(values[0], values[1]);
        }
    }

I want to use two arraylist or something similar because I will later use

Arraylist emails=new Arraylist();
Arraylist passwords=new Arraylis();
foreach(string email in emails)
foreach(string password in passwords)
{
sending multiple emails...
}

you have writein your code
string password = kvp.Password;

did you mean
string password = kvp.Value

because I get error

how would you filter emails and passwordin Dictionary by provider(gmail,hotmail,yahoo)????

 foreach (KeyValuePair<string, string> kvp in accounts)
            {
                if(kvp.Key.Contains("gmail"))
                {
//mail....
                 }

other way:

Dictionary<string, string> emails = new Dictionary<string, string>();

foreach (string combo in File.ReadAllLines(@"C:\User\Comp\Desktop\file.txt"))
{
    string[] values = combo.Split(':');
    if (values.Length >= 2)
    {
        // Filter here... for example...
        if (values[0].Containsh("gmail"))
        {
            // Now your emails will only be added if they match your criteria...
            emails.Add(values[0], values[1]);
        }
    }

Your suggested algorithm won't work the way you want it to work.  Let's say we have this:

bob:Swordfish
jim:Alligator
frank:FriedFish

Now, when you do nested foreach statements like you're trying to do, you'll end up with the inner loop with the passwords going completely through the list before going on to the next email, which means, you'll send every email to the first person, then every email to the second person and so on.  Given the data above, this would happen:

email sent to - password sent in email
bob - Swordfish
bob - Alligator
bob - Friedfish
jim - Swordfish
jim - Alligator
jim - Friedfish
frank - Swordfish
frank - Alligator
frank - Friedfish

Obviously, they don't all share their passwords. 

The Dictionary<string, string> is still what you need.  Watch how I've fleshed out the code below:

Dictionary<string, string> passwords = new Dictionary<string, string>();

foreach (string combo in File.ReadAllLines("file.txt"))
{
    string[] values = combo.Split(':');
    if (values.Length >= 2)
        passwords.Add(values[0], values[1]);
}

foreach (KeyValuePair<string, string> kvp in passwords)
{
    string email = kvp.Key;
    string password = kvp.Value;
    // send an email using the specified email and password
}


A dictionary will maintain the relationship between the email and the password, which is really what you want to do.  I'm assuming you don't want to send out all the passwords to all the users.

Go look up Dictionary<TKey, TValue> on google.  Click the first link.

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