Sending an email on behalf of the user without compose window

As the title says, is there a way to send an email on behalf of the user without the compose window showing and requiring the user to click on “Send”? I know this was possible with previous versions of Thunderbird, but I cannot find the option in the WebExtensions documentations.

For example, this was how it was done before:

// Initialization of the message to be sent with various parameters
var msgCompose = (typeof(msgComposeService[‘InitCompose’]) != ‘undefined’) ? msgComposeService.InitCompose(null, params) : msgComposeService.initCompose(params); // comm-1.9.2 or comm-central
var nsIMsgCompDeliverMode = Components.interfaces.nsIMsgCompDeliverMode;
//msgCompose.currentHeaderData[‘content-type’].headerValue = ‘multipart/report;’;

	return msgCompose.SendMsg( // Sends the message to the recipient
		ioService.offline ? nsIMsgCompDeliverMode.Later : nsIMsgCompDeliverMode.Now,