Receipt address won't show up in the email sent by golang smtp client

Here is the code snippet to send the email via a local postfix server:

from := r.FormValue("from")
to := strings.Split(r.FormValue("to"), ";")
body := r.FormValue("body")
mime := "MIME-version:1.0;\nContent-Type:text/html;charset=\"UTF-8\";\n\n"
subject := fmt.Sprintf("Subject: %s\n", r.FormValue("subject"))
msg := []byte(subject + mime + body)

err := smtp.SendMail("localhost:25", nil, from, to, msg)

The email was sent/received fine. However, it is missing the receipt address in the To field of received email. I also tried it on an exchange server. The receipt addresses are missing as well. Here is what it shows in the email source.

To: Undisclosed recipients:;

Any suggestions to fix it? thanks!

You're setting the values for the mail envelope, but you haven't put any headers in the email itself except for Subject:. You should also be using \r\n as a newline for email.

A minimal example might look like:

headers := make(map[string]string)

headers["Subject"] = "this is a test"
headers["From"] = "me@example.com"
headers["To"] = "you@example.com"

body := "hello,\nthis is a test"

var msg bytes.Buffer
for k, v := range headers {
	msg.WriteString(k + ": " + v + "\r\n")
}

msg.WriteString("\r\n")
msg.WriteString(body)

Some other helpful stdlib packages:

• net/textproto for MIME header handling
• net/mail for address handling (though the package is really only for parsing email)
• http://gopkg.in/gomail.v1 for a more complete solution (there are probably many others)