Go Golang SMTP Script. Need to add BCC header - go

Question

I am using this well known blank canvas for SMTP in Go.
I need to add in Bcc Blank Carbon Copy address to it but I have tried lots of things and nothing I am trying works which is strange...
I have tried adding in "headers["Bcc"] = "someemail#address.com" I am sure it is an easy modification.
Thanks in Advance..
package main
import (
"fmt"
"log"
"net"
"net/mail"
"net/smtp"
"crypto/tls"
)
func main() {
from := mail.Address{"", "username#example.tld"}
to := mail.Address{"", "username#anotherexample.tld"}
subj := "This is the email subject"
body := "This is an example body.\n With two lines."
headers := make(map[string]string)
headers["From"] = from.String()
headers["To"] = to.String()
headers["Subject"] = subj
message := ""
for k,v := range headers {
message += fmt.Sprintf("%s: %s\r\n", k, v)
}
message += "\r\n" + body
servername := "smtp.example.tld:465"
host, _, _ := net.SplitHostPort(servername)
auth := smtp.PlainAuth("","username#example.tld", "password", host)
tlsconfig := &tls.Config {
InsecureSkipVerify: true,
ServerName: host,
}
conn, err := tls.Dial("tcp", servername, tlsconfig)
if err != nil {
log.Panic(err)
}
c, err := smtp.NewClient(conn, host)
if err != nil {
log.Panic(err)
}
if err = c.Auth(auth); err != nil {
log.Panic(err)
}
if err = c.Mail(from.Address); err != nil {
log.Panic(err)
}
if err = c.Rcpt(to.Address); err != nil {
log.Panic(err)
}
w, err := c.Data()
if err != nil {
log.Panic(err)
}
_, err = w.Write([]byte(message))
if err != nil {
log.Panic(err)
}
err = w.Close()
if err != nil {
log.Panic(err)
}
c.Quit()
}

Answer 1

See the following segment from the smtp#SendMail package docs
The msg parameter should be an RFC 822-style email with headers first, a blank line, and then the message body. The lines of msg should be CRLF terminated. The msg headers should usually include fields such as "From", "To", "Subject", and "Cc". Sending "Bcc" messages is accomplished by including an email address in the to parameter but not including it in the msg headers.
In other words, don't add them in the headers, just to the recepient list.
In your example boilerplate code, you would add a call to c.Rcpt(...) for each email in the bcc list, and that's it. Nothing to add to headers.

Answer 2

You need to add a RCPT line for the Bcc address too, for example:
if err = c.Rcpt("someemail#address.com"); err != nil {
log.Panic(err)
}

Answer 3

as user10753492 pointed out, the standard doesn't include the concepts of carbon copies. You'd need to add one RCPT TO for each recipient and then add bcc: sample#email.com to the body. The client will take care of the rest.