(.NET Core C#) GMail SMTP Send using Previously Obtained OAuth2 Access Token

Demonstrates how to send email using GMail and OAuth2 authentication. This example assumes an OAuth2 access token was previously obtained.

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

// See Get GMail SMTP Access Token 
// for sample code showing how to obtain a GMail SMTP access token for desktop apps.

// In this example, our access token was previously saved to the following file which contains JSON like this:
// 	{
// 	 "access_token": "ya39.Ci-XA_C5bGgRDC3UaD-h0_NeL-DVIQnI2gHtBBBHkZzrwlARkwX6R3O0PCDEzRlfaQ",
// 	 "token_type": "Bearer",
// 	 "expires_in": 3600,
// 	 "refresh_token": "1/r_2c_7jddspcdfesrrfKqfXtqo08D6Q-gUU0DsdfVMsx0c"
// 	}
// 
Chilkat.JsonObject json = new Chilkat.JsonObject();
bool success = json.LoadFile("qa_data/tokens/_gmailSmtp.json");
if (success != true) {
    Debug.WriteLine("Failed to load GMail access token file.");
    return;
}

string accessToken = json.StringOf("access_token");

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

// Set the properties for the GMail SMTP server:
mailman.SmtpHost = "smtp.gmail.com";
mailman.SmtpPort = 587;
mailman.StartTLS = true;

// The SMTP username should be the GMail address of the user's account that authorized your app to send email.
mailman.SmtpUsername = "chilkat.support@gmail.com";
mailman.OAuth2AccessToken = accessToken;

// 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 = "Chilkat <chilkat.support@gmail.com>";
email.AddTo("Chilkat Admin","admin@chilkatsoft.com");
// To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

// 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;
}

// You may close the connection here.  If the connection is kept open, 
// the next call to mailman.SendEmail will continue using the already-established connection
// (and automatically re-connect if needed).
success = mailman.CloseSmtpConnection();
if (success != true) {
    Debug.WriteLine("Connection to SMTP server not closed cleanly.");
}

Debug.WriteLine("Email Sent via GMail with OAuth2 authentication.");