使用Go将电子邮件标头包含在应用程序引擎中吗？

Question

The google app engine documentation doesn't describe how to include an email header, how do you do it, i.e. How do you change this?

    msg := &mail.Message{
            Sender:  "Example.com Support <[e-mail]>",
            To:      []string{"[e-mail]"},
            Subject: "Confirm your registration",
            Body:    fmt.Sprintf(confirmMessage, url),
    }
    if err := mail.Send(c, msg); err != nil {
            c.Errorf("Couldn't send email: %v", err)
    }

Answer 1

In the appengine/mail reference you can find that type Message has a field called Headers:

// Extra mail headers.
// See https://developers.google.com/appengine/docs/go/mail/overview
// for permissible headers.
Headers mail.Header

The type mail.Header can be found in the net/mail package, and only the following header names may be used, as described in the above overview link:

• In-Reply-To
• List-Id
• List-Unsubscribe
• On-Behalf-Of
• References
• Resent-Date
• Resent-From
• Resent-To

Example: (untested)

import netmail "net/mail" // mail is already taken by appengine/mail

...

msg := &mail.Message{
        Sender:  "Example.com Support <[e-mail]>",
        To:      []string{"[e-mail]"},
        Subject: "Confirm your registration",
        Body:    fmt.Sprintf(confirmMessage, url),
        Headers:  netmail.Header{"In-Reply-To": []string{"123456789"}},
}