Thanks, both sdgrahamadn owlman5. So it is fine to write 'I apologize for the lenthy email‘ if i put it at the end of my email?I missed "at the end" in your first post, stcopy. I agree with the others that this is the wrong place to use that sentence.
Your sentence is fine at the beginning of the email. That way, you are apologizing "in advance" for the length of the following email.