(C#) OAuth2 for a GMail using a P12 Service Account Key

See more GMail REST API Examples

Note: This example does not work for Personal Google Accounts where the email domain is @gmail.com

For more information, see https://www.chilkatsoft.com/google_workspace_setup_smtp_gmail.asp

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

Chilkat.Http http = new Chilkat.Http();

// --------------------------------------------------------------------------------
// For a step-by-step guide for setting up your Google Workspace service account,
// see Setup Google Workspace Account for Sending SMTP GMail from a Service Account
// --------------------------------------------------------------------------------
// Begin by loading your Google service account key (.p12)
Chilkat.Cert cert = new Chilkat.Cert();
bool success = cert.LoadPfxFile("c:/someDirectory/keys/chilkat25-cbd7b42afbd8.p12","notasecret");
if (success != true) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

// The ISS is your service account email address ending in gserviceaccount.com.
string iss = "chilkatsvc@chilkat25.iam.gserviceaccount.com";

// The scope is always the following string:
string scope = "https://mail.google.com/";

// The sub is your company email address
string oauth_sub = "bob@yourcompany.com";

// The access token is valid for this number of seconds.
int numSec = 3600;

string accessToken = http.G_SvcOauthAccessToken(iss,scope,oauth_sub,numSec,cert);
if (http.LastMethodSuccess != true) {
    Debug.WriteLine(http.LastErrorText);
    return;
}
else {
    Debug.WriteLine("access token: " + accessToken);
}

// The access token allows us to send unlimited emails while it's valid. Once it expires, we must obtain and use a new one.

// -----------------------------------------------------------------------
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;

mailman.SmtpUsername = "bob@yourcompany.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 = "Bob <bob@yourcompany.com>";
success = email.AddTo("Recipient","recipient@example.com");
// To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

success = mailman.SendEmail(email);
if (success != true) {
    Debug.WriteLine(mailman.LastErrorText);
    return;
}

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

Debug.WriteLine("Successfully sent email using Gmail with a service account key.");