The bulk message error is automatically generated by the system and it would not give a false alarm. The message count also includes the number of bounce backs that sender receives which we do not keep them in the logs.
This may sound counter intuitive at first, but depending on how many recipients exist in the message, the email as a whole might get rejected and not just any random number of people in the recipient fields. For a sender who have not sent anything in the previous 10 minutes, the Sentinel Messaging rate limiting system will start rejecting recipients after 100 is reached(100 emails per 10 minutes limit- for more information about acceptable use policy for outbound Click here), and those individual rejects count toward the SMTP session’s total error count. The maximum allowed error count is variable depending on the server load, but once that is reached, the whole email gets rejected.