minor improvement to submit alternatives without array

Instead of 
var options = {
    sender: 'Sender sender@example.com',
    to: '"Receiver" receiver@example.com',
    subject: 'Appointment',
    text: 'Appointment Plain',
    html: 'Appointment HTML',
    alternative : [
        {
            contentType: "text/calendar; method=REQUEST; name="meeting.ics"",
            contents: new Buffer(...),
            contentEncoding: 7bit
        }
    ]
}; 

you could also write:

var options = {
    sender: 'Sender sender@example.com',
    to: '"Receiver" receiver@example.com',
    subject: 'Appointment',
    text: 'Appointment Plain',
    html: 'Appointment HTML',
    alternative : 
        {
            contentType: "text/calendar; method=REQUEST; name="meeting.ics"",
            contents: new Buffer(...),
            contentEncoding: 7bit
        }
};