(.NET Core C#) Office365 Send Email using SMTP with OAuth2 Authentication

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Demonstrates how to send email from smtp.office365.com using OAuth2 authentication.

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// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// An Office365 OAuth2 access token must first be obtained prior
// to running this code.

// Getting the OAuth2 access token for the 1st time requires the O365 account owner's 
// interactive authorization via a web browser.  Afterwards, the access token
// can be repeatedly refreshed automatically (with no user interaction).

// See the following examples for getting and refreshing an OAuth2 access token

// Get Office365 SMTP/IMAP/POP3 OAuth2 Access Token
// Refresh Office365 SMTP/IMAP/POP3 OAuth2 Access Token

// First get our previously obtained OAuth2 access token.
Chilkat.JsonObject jsonToken = new Chilkat.JsonObject();
bool success = jsonToken.LoadFile("qa_data/tokens/office365.json");

Chilkat.MailMan mailman = new Chilkat.MailMan();

mailman.SmtpHost = "smtp.office365.com";
mailman.SmtpPort = 587;
mailman.StartTLS = true;

// Use your Office365 email address for the SmtpUsername.
mailman.SmtpUsername = "OFFICE365_EMAIL_ADDRESS";
mailman.OAuth2AccessToken = jsonToken.StringOf("access_token");

// Create a new email object
Chilkat.Email email = new Chilkat.Email();

email.Subject = "This is a test";
email.Body = "This is a test";
email.From = "MY_NAME <OFFICE365_EMAIL_ADDRESS>";
success = email.AddTo("John Doe","somebody@example.com");

// Call SendEmail to connect to the SMTP server and send.
// The connection (i.e. session) to the SMTP server remains
// open so that subsequent SendEmail calls may use the
// same connection.  
success = mailman.SendEmail(email);
if (success != true) {
    Debug.WriteLine(mailman.LastErrorText);
    return;
}

// If SendEmail failed because of "Failed to get initial SMTP Response", then it may be 
// a firewall or anti-virus blocking communications.
// See https://cknotes.com/smtp-office365-com-failed-to-get-initial-smtp-response/

success = mailman.CloseSmtpConnection();
if (success != true) {
    Debug.WriteLine("Connection to SMTP server not closed cleanly.");
}

Debug.WriteLine("Mail Sent!");