It is Latin, but it is also an English word. But as Maidhc implies, it wouldn't be understood by most native English speakers. I would resend the email with 'Corrected' at the beginning of the Subject. I would write Corrected: at the beginning of the subject, and write a small note at the beginning of the email to explain that the first version had a mistake, but this version has been corrected. corrigendum literally means: 'a thing to be corrected'

That's a mouthful, and an unfamiliar one. An English writer would use "erratum", and only explain the error. Eg. Erratum: The sentence "Due on the 25th of September" should read "Due on the 25th of October".

That's not English. Is it Latin? I think there's an Answers section for questions on Latin as well.