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1.
when you form a chat-like conversation over the email with one or more people by simply replying again and again to the same message. Each reply is usually a question or something thought-provoking, prompting the other person to respond as well. They can get pretty long.
"dude, here they don't allow chatting on the school computers, so i usually get by talking to her with these huge-ass email trains each morning."

by Ghostface-killah May 17, 2007