Sending a list of emails using SmtpClient

I am using SendCompletedEventHandler from SmtpClient when sending a list of emails.

SendCompletedEventHandler is only called when all emails in the list have already been sent.

I have expexted that SendCompletedEventHandler is called when an email is sent.

Is there something wrong with my code?

    public void SendAllNewsletters(List<string> recipients)
    {
        string mailText  = "My Text";
        foreach(string recipient in recipients)
        {
            //if this loop takes 10min then the first call to
            //SendCompletedCallback is after 10min
            SendNewsletter(mailText,recipient);
        }
    }

    public bool SendNewsletter(string mailText , string emailaddress)
    {

            SmtpClient sc = new SmtpClient(_smtpServer, _smtpPort);
            System.Net.NetworkCredential SMTPUserInfo = new System.Net.NetworkCredential(_smtpuser, _smtppassword);
            sc.Credentials = SMTPUserInfo;
            sc.SendCompleted += new SendCompletedEventHandler(SendCompletedCallback);

            MailMessage mm = null;
            mm = new MailMessage(_senderemail, emailaddress );
            mm.IsBodyHtml = true;
            mm.Priority = MailPriority.Normal;
            mm.Subject = "Something";
            mm.Body = mailText ;
            mm.SubjectEncoding = Encoding.UTF8;
            mm.BodyEncoding = Encoding.UTF8;

            //Mail 
            string userState = emailaddress;
            sc.SendAsync(mm, userState);

            return true;
    }


    public void SendCompletedCallback(object sender, AsyncCompletedEventArgs e)
    {
        // Get the unique identifier for this asynchronous operation.
        String token = (string)e.UserState;
        if (e.Error != null)
        {
            _news.SetNewsletterEmailsisSent(e.UserState.ToString(), _newslettername, false, e.Error.Message); 
        }
        else
        {
            _news.SetNewsletterEmailsisSent(e.UserState.ToString(), _newslettername, true, string.Empty);
        }            
    }