Highlights in Header Column

Can anyone tell me what it means when the Headers colum shows ,\nContent-type: text/html; charset=UTF-8 as highlighted in yellow? It seems to correspond with that message not actually being received by the recipient but I’m struggling to understand why since there are no errors associated with the message in either view. I’ve been playing with my cron configurations and other optimizations but it seemed odd that the messages that were highlighted in that view also were never received.