MailWorkerChan := make(chan int, workerConfig.Mail)

func SendMailList(L []*model.Mail) {
    for _, mail := range L {
        MailWorkerChan <- 1
        go SendMail(mail)
    }
}

func SendMail(mail *model.Mail) {
    defer func() {
        <-MailWorkerChan
    }()

    url := g.Config().Api.Mail
    r := httplib.Post(url).SetTimeout(5*time.Second, 30*time.Second)
    r.Param("tos", mail.Tos)
    r.Param("subject", mail.Subject)
    r.Param("content", mail.Content)
    resp, err := r.String()
    if err != nil {
        log.Errorf("send mail fail, receiver:%s, subject:%s, cotent:%s, error:%v", mail.Tos, mail.Subject, mail.Content, err)
    }

    log.Debugf("send mail:%v, resp:%v, url:%s", mail, resp, url)
}

该代码节选自open-falcon的alarm模块中发送邮件的部分，主要通过MailWorkerChan实现控制速率。