(For incoming mails that have not been processed correctly due to any runtime error) The Email Engine considers the HTML format, by default. If the incoming message is in a plain text format, Email Engine first checks for the HTML format and when not found, considers the plain text format. But, if the incoming mail is in a plain text as well as HTML format, the Email Engine only considers the HTML format. For the Email Engine to consider the plain text format, change the HTML format to a plain text format (without any spaces) or clear the HTML format.