Therefore, trail mail means nothing but a copy of your previous email. Here the writer includes your previous email while replying or forwarding it to you, with his additional write-up.

How do you reply to trailing mail?

When reply a trail mail ( A mail which you are replying again and again) , be sure the subject has changed when you are discussing another topic. When you follow or reply to a mail you got and if you follow the same thread you must take care of the subject.

What is a trailing message?

email. Sometimes, I see the expression of "trailing emails" in business emails. I understand it means all previous emails between correspondents hanging from the most recent email.