MimeKit not able to send emails using SES SMTP

I developed a C# application that uses MimeKit to send emails through SES. The following code demonstrates this Note: My server only allows the port - 25.

        public virtual bool Send(MimeMail mimeMail)
    {
        try
        {
            mimeMailSmtpClient = new MailKit.Net.Smtp.SmtpClient();
            mimeMailSmtpClient.Connect("email-smtp.us-west-2.amazonaws.com", 25,SecureSocketOptions.StartTls);
            mimeMailSmtpClient.Authenticate(serverUsername, serverPassword);
            mimeMailSmtpClient.Send(mimeMail.GetMessageItem());
            mimeMailSmtpClient.Disconnect(true);
   
            return true;
        }
        catch (Exception ex)
        {
            var msg = ex.Message;
            return false;
        }
    }

When I execute my email sending function, I receive the following error:

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

The server's SSL certificate could not be validated for the following reasons:
• The server certificate has the following errors:
  • The revocation function was unable to check revocation for the certificate.

  • The revocation function was unable to check revocation because the revocation server was offline.

• An intermediate certificate has the following errors:
  • The revocation function was unable to check revocation for the certificate.

  • The revocation function was unable to check revocation because the revocation server was offline.

• An intermediate certificate has the following errors:
  • The revocation function was unable to check revocation for the certificate.

  • The revocation function was unable to check revocation because the revocation server was offline.

• An intermediate certificate has the following errors:
  • The revocation function was unable to check revocation for the certificate.

  • The revocation function was unable to check revocation because the revocation server was offline.

In PowerShell, I tried to enter the following command to connect to the Amazon SES SMTP server:

It connected successfully.

Am I missing any enabling part in my C# code?

Thanks

Change your code to either of these.

Disable SSL/TLS certificate revocation checks:

public virtual bool Send(MimeMail mimeMail)
{
    try
    {
        mimeMailSmtpClient = new MailKit.Net.Smtp.SmtpClient();
        mimeMailSmtpClient.CheckCertificateRevocation = false;
        mimeMailSmtpClient.Connect("email-smtp.us-west-2.amazonaws.com", 25,SecureSocketOptions.StartTls);
        mimeMailSmtpClient.Authenticate(serverUsername, serverPassword);
        mimeMailSmtpClient.Send(mimeMail.GetMessageItem());
        mimeMailSmtpClient.Disconnect(true);
   
        return true;
    }
    catch (Exception ex)
    {
        var msg = ex.Message;
        return false;
    }
}

or disable STARTTLS:

public virtual bool Send(MimeMail mimeMail)
{
    try
    {
        mimeMailSmtpClient = new MailKit.Net.Smtp.SmtpClient();
        mimeMailSmtpClient.Connect("email-smtp.us-west-2.amazonaws.com", 25,SecureSocketOptions.None);
        mimeMailSmtpClient.Authenticate(serverUsername, serverPassword);
        mimeMailSmtpClient.Send(mimeMail.GetMessageItem());
        mimeMailSmtpClient.Disconnect(true);
   
        return true;
    }
    catch (Exception ex)
    {
        var msg = ex.Message;
        return false;
    }
}