 <p>I figure it out. I was using a helper written by a third party. I went with what with SendGrid actually suggested. See code below that is now working.</p> <pre><code>var myMessage = new SendGridMessage {From = new MailAddress("info@email.com")}; myMessage.AddTo("Jeff Kennedy &lt;info@info.com&gt;"); myMessage.Subject = "test email"; myMessage.Html = "&lt;p&gt;See Attachedment for Lead&lt;/p&gt;"; myMessage.Text = "Hello World plain text!"; myMessage.AddAttachment("C:\\tblaccudatacounts.csv"); var apiKey = "apikey given by sendgrid"; var transportWeb = new Web(apiKey); await transportWeb.DeliverAsync(myMessage); </code></pre>