SmtpClient with Gmail

Question

I\'m developing a mail client for a school project. I have managed to send e-mails using the SmtpClient in C#. This works perfectly with any server but it doesn

Answer 1

Gmail's SMTP server requires you to authenticate your request with a valid gmail email/password combination. You do need SSL enabled as well. Without actually being able to see a dump of all your variables being passed in the best guess I can make is that your Credentials are invalid, make sure you're using a valid GMAIL email/password combination.

You might want to read here for a working example.

EDIT: Okay here's something I wrote and tested just then and it worked fine for me:

public static bool SendGmail(string subject, string content, string[] recipients, string from) {
    if (recipients == null || recipients.Length == 0)
        throw new ArgumentException("recipients");

    var gmailClient = new System.Net.Mail.SmtpClient {
        Host = "smtp.gmail.com",
        Port = 587,
        EnableSsl = true,
        UseDefaultCredentials = false,
        Credentials = new System.Net.NetworkCredential("******", "*****")
    };

    using (var msg = new System.Net.Mail.MailMessage(from, recipients[0], subject, content)) {
        for (int i = 1; i < recipients.Length; i++)
            msg.To.Add(recipients[i]);

        try {
            gmailClient.Send(msg);
            return true;
        }
        catch (Exception) {
            // TODO: Handle the exception
            return false;
        }
    }
}

If you need any more info there's a similar SO article here

Answer 2

I think, you need to validate the server certificate that is used to establish the SSL connections.....

Use following code to send mail with validating server certificate.....

            this.client = new SmtpClient(_account.SmtpHost, _account.SmtpPort);
            this.client.EnableSsl = _account.SmtpUseSSL;
            this.client.Credentials = new NetworkCredential(_account.Username, _account.Password);

        try
        {
            // Create instance of message
            MailMessage message = new MailMessage();

            // Add receivers
            for (int i = 0; i < email.Receivers.Count; i++)
                message.To.Add(email.Receivers[i]);

            // Set sender
            message.From = new MailAddress(email.Sender);

            // Set subject
            message.Subject = email.Subject;

            // Send e-mail in HTML
            message.IsBodyHtml = email.IsBodyHtml;

            // Set body of message
            message.Body = email.Message;

            //validate the certificate
            ServicePointManager.ServerCertificateValidationCallback =
            delegate(object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
            { return true; };


            // Send the message
            this.client.Send(message);

            // Clean up
            message = null;
        }
        catch (Exception e)
        {
            Console.WriteLine("Could not send e-mail. Exception caught: " + e);
        }

Import System.Security.Cryptography.X509Certificates namespace to use ServicePointManager

Answer 3

I started getting this with GMail in May 2013 after working for 6 momths. The Mono project's Using Trusted Roots Respectfully document provided guidance on work around. I chose option #1:

ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

It is too disruptive to have e-mail for my service stop working without warning.

Update Aug 26 2016: user Chico suggested the following complete implementation of the ServerCertificateValidationCallback callback. I have not tested.

ServicePointManager.ServerCertificateValidationCallback = MyRemoteCertificateValidationCallback;

bool MyRemoteCertificateValidationCallback(System.Object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) {
    bool isOk = true;
    // If there are errors in the certificate chain, look at each error to determine the cause.
    if (sslPolicyErrors != SslPolicyErrors.None) {
        for (int i=0; i<chain.ChainStatus.Length; i++) {
            if (chain.ChainStatus [i].Status != X509ChainStatusFlags.RevocationStatusUnknown) {
                chain.ChainPolicy.RevocationFlag = X509RevocationFlag.EntireChain;
                chain.ChainPolicy.RevocationMode = X509RevocationMode.Online;
                chain.ChainPolicy.UrlRetrievalTimeout = new TimeSpan (0, 1, 0);
                chain.ChainPolicy.VerificationFlags = X509VerificationFlags.AllFlags;
                bool chainIsValid = chain.Build ((X509Certificate2)certificate);
                if (!chainIsValid) {
                    isOk = false;
                }
            }
        }
    }
    return isOk;

}

Answer 4

You need to enable 2-Step Verification in your gmail account and create an app password (https://support.google.com/accounts/answer/185833?hl=en). Once you replace your password with the new app password, it should work.

Credentials = new System.Net.NetworkCredential("your email address", "your app password");

Answer 5

Try running this:

mozroots --import --ask-remove

in your system (just in bash or from Mono Command Prompt if it is on Windows). And then run the code again.

EDIT:

I forgot you also should run

certmgr -ssl smtps://smtp.gmail.com:465

(and answer yes on questions). This works for me on Mono 2.10.8, Linux (with your example).

Answer 6

This code works fine for me, try pasting this into LinqPad, edit the mail addresses and password and tell us what you see:

var client = new System.Net.Mail.SmtpClient("smtp.gmail.com", 587);
client.EnableSsl = true;
client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential("me@gmail.com", "xxxxxxx");

try
{
    // Create instance of message
    System.Net.Mail.MailMessage message = new System.Net.Mail.MailMessage();

    // Add receiver
    message.To.Add("me@gmail.com");

    // Set sender
    // In this case the same as the username
    message.From = new System.Net.Mail.MailAddress("me@gmail.com");

    // Set subject
    message.Subject = "Test";

    // Set body of message
    message.Body = "En test besked";

    // Send the message
    client.Send(message);

    // Clean up
    message = null;
}
catch (Exception e)
{
    Console.WriteLine("Could not send e-mail. Exception caught: " + e);
}