code: @Nonnegative
    public int queueMails (@Nonnull final ISMTPSettings aSMTPSettings,
                           @Nonnull final Collection <? extends IMutableEmailData> aMailDataList)
    {
      return MailAPI.queueMails (aSMTPSettings, aMailDataList);
    }
docs: Queue multiple mails at once.
  
  @param aSMTPSettings
  The SMTP settings to be used.
  @param aMailDataList
  The mail messages to queue. May not be <code>null</code>.
  @return The number of queued emails. Always &ge; 0. Maximum value is the
  number of {@link IMutableEmailData} objects in the argument.