The following things are considered while checking:
The time delay between messages re-sending (repeat_delay);
Message sending delay (after_delay);
Auto messages triggers;
Events "message sent" and "message read" which are created by message.
There should be a time period for at least 30 seconds between two events. If this condition was not followed we will show a warning pop-up, so you will need to confirm the action.
Such cycles can be correct when you set audience which is not considered in cycled analysis.
You created an email with "Communication: Message sent" trigger. By sending this email a custom "Message №1 sent" event is created.
You set "Message №1 sent" event as a trigger for another message.
So, the second message will be sent after the first one (and auto message sending will trigger the first message as well). It turns into the loop. Auto message cycles can be long or short (message can loop itself).
The limit for events number
Since there is a technical possibility to create a cycle, we expose a limit for the number of events (for one lead): no more than 60 events per minute. We block leads who exceed the quota until the number of events won't reduce to acceptable 60 per minute.