how to send email using MailKit in Asp.Net Core

Question

Am not sure whether the old method of sending Mail using Mailkit is quite working with this code below

try
            {
                var emailMessage = new MimeMessage();
                emailMessage.From.Add(new MailboxAddress(_emailConfig.SenderName, _emailConfig.SenderAddress));
                emailMessage.To.Add(new MailboxAddress(email));
                emailMessage.Subject = subject;
                var builder = new BodyBuilder
                {
                    HtmlBody = message
                };
                emailMessage.Body = builder.ToMessageBody();
                using var smtp = new SmtpClient
                {
                    ServerCertificateValidationCallback = (s, c, h, e) => true
                };
                smtp.AuthenticationMechanisms.Remove("XOAUTH2");

                await smtp.ConnectAsync(_emailConfig.SmtpServer, Convert.ToInt32(_emailConfig.Port), false).ConfigureAwait(false);
                await smtp.AuthenticateAsync(_emailConfig.Username, _emailConfig.Password).ConfigureAwait(false);
                await smtp.SendAsync(emailMessage).ConfigureAwait(false);
                await smtp.DisconnectAsync(true).ConfigureAwait(false);
            }
            catch (Exception ex)
            {
                throw new InvalidOperationException(ex.Message);
            }

but am having exceptions if i use the code above to send email

nvalidOperationException: 534: 5.7.14 <https://accounts.google.com/signin/continue?sarp=1&scc=1&plt=AKgnsbv
5.7.14 26mzQKtlwfyEdGzHHdpi3ewWG6skAWgOBbdNNYmwzr9Sg3fGu-KixLAfODpJsVafutidE
5.7.14 8xBOp_8rNCvk9Y6iEcOkDlcZ1d-483zQ1Krw04NvqxQdq3w4iTtC8E9bL8uGprgV>
5.7.14 Please log in via your web browser and then try again.
5.7.14 Learn more at
5.7.14 https://support.google.com/mail/answer/78754 o5sm2555896wmh.8 - gsmtp

so when i changed this line of code below to use SSLS, A new error came out

await smtp.ConnectAsync(_emailConfig.SmtpServer, Convert.ToInt32(_emailConfig.Port), true).ConfigureAwait(false);

Exception returned

InvalidOperationException: An error occurred while attempting to establish an SSL or TLS connection.

This usually means that the SSL certificate presented by the server is not trusted by the system for one or more of
the following reasons:

1. The server is using a self-signed certificate which cannot be verified.
2. The local system is missing a Root or Intermediate certificate needed to verify the server's certificate.
3. A Certificate Authority CRL server for one or more of the certificates in the chain is temporarily unavailable.
4. The certificate presented by the server is expired or invalid.

Another possibility is that you are trying to connect to a port which does not support SSL/TLS.

It is also possible that the set of SSL/TLS protocols supported by the client and server do not match.

See https://github.com/jstedfast/MailKit/blob/master/FAQ.md#SslHandshakeException for possible solutions.

have searched everywhere on how to do it,even turned on my less secured app. some recommended sendGrid, i created a free account with them also,but i dont have access to the account created. Does anyone knows how to fix the code above using Mailkit

Answer 1

Try it like this.

using (var smtpClient = new SmtpClient())
{
   smtpClient.ServerCertificateValidationCallback = (s, c, h, e) => true;
   await smtpClient.ConnectAsync("host", port, false);

   if (smtpClient.Capabilities.HasFlag(SmtpCapabilities.Authentication))
   {
      smtpClient.AuthenticationMechanisms.Remove("XOAUTH2");
      await smtpClient.AuthenticateAsync(username, password);
   }

   await smtpClient.SendAsync(mailMsg);
   smtpClient.Disconnect(true);
}