(.NET Core C#) Send HTML Email with CSS as Related Item using Content-Location

Demonstrates how to compose an HTML email with an external CSS file included as a related item and referenced by Content-Location.

Some email clients display embedded (related) content best using CID's (Content-IDs), whereas other email clients display related content best by Content-Location. The choice you make may depend on the software used by the intended recipient of your email. (Does' the recipient read email on an iPhone? Android? Outlook? GMail? Thunderbird? etc.)

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

// The mailman object is used for sending and receiving email.
Chilkat.MailMan mailman = new Chilkat.MailMan();

// Use your SMTP server hostname.  This example uses office365, but it could be any SMTP server..
mailman.SmtpHost = "outlook.office365.com";
mailman.SmtpPort = 587;
mailman.StartTLS = true;

// Set the SMTP login/password
mailman.SmtpUsername = "OFFICE365-SMTP-LOGIN";
mailman.SmtpPassword = "OFFICE365-SMTP-PASSWORD";

// Create a new email object
Chilkat.Email email = new Chilkat.Email();
email.Subject = "HTML Email with embedded CSS";
email.From = "Chilkat Support <my-office365-user@mydomain.com>";
email.AddTo("Chilkat Support","support@chilkatsoft.com");

Chilkat.StringBuilder sbCss = new Chilkat.StringBuilder();
bool bCrlf = true;
sbCss.AppendLine("body {",bCrlf);
sbCss.AppendLine("    background-color: powderblue;",bCrlf);
sbCss.AppendLine("}",bCrlf);
sbCss.AppendLine("h1 {",bCrlf);
sbCss.AppendLine("    color: blue;",bCrlf);
sbCss.AppendLine("}",bCrlf);
sbCss.AppendLine("p {",bCrlf);
sbCss.AppendLine("    color: red;",bCrlf);
sbCss.AppendLine("}",bCrlf);

// The filenameInHtml is what should exists within the HTML (in the href atribute)
string filenameInHtml = "styles.css";
// Call AddRelatedString2 to use Content-Location.
email.AddRelatedString2(filenameInHtml,sbCss.GetAsString(),"utf-8");

Chilkat.StringBuilder sbHtml = new Chilkat.StringBuilder();
sbHtml.AppendLine("<!DOCTYPE html>",bCrlf);
sbHtml.AppendLine("<html>",bCrlf);
sbHtml.AppendLine("<head>",bCrlf);
sbHtml.AppendLine("  <link rel=\"stylesheet\" href=\"styles.css\">",bCrlf);
sbHtml.AppendLine("</head>",bCrlf);
sbHtml.AppendLine("<body>",bCrlf);
sbHtml.AppendLine("",bCrlf);
sbHtml.AppendLine("<h1>This is a heading</h1>",bCrlf);
sbHtml.AppendLine("<p>This is a paragraph.</p>",bCrlf);
sbHtml.AppendLine("",bCrlf);
sbHtml.AppendLine("</body>",bCrlf);
sbHtml.AppendLine("</html>",bCrlf);

email.SetHtmlBody(sbHtml.GetAsString());

bool success = mailman.SendEmail(email);
if (success != true) {
    Debug.WriteLine(mailman.LastErrorText);
}
else {
    Debug.WriteLine("Mail Sent!");
}