Ah. I see. The problem is that your email is putting line breaks in places where it shouldn't. It probably has to do with screen width or something on the server that reads multiline text as actually having line breaks when it really doesn't. If you remove those line breaks, then it verifies.
Thank you for clarifying. 
FYI, the cause of this problem are not related with the screen width or something on the server that reads multi-line text like what you said (bolded text) in the quoted message.
They(Google) are just following the internet standard for plain text messages (RFC 2822) recommended and promoted by the Internet Engineering Task Force (IETF) where maximum characters per line in the source of email messages should be no more than 78.
Read here: https://mathiasbynens.be/notes/gmail-plain-text
#stillwaiting #verybusy