An e-mail program that consolidates messages with the same subject line so they appear together. Both e-mail client programs and Web-based e-mail offer threaded e-mail. Non-Threaded Mail Keeps Duplicating If e-mail is not threaded, each new reply in a conversation appears in the inbox as a new message. As long as users reply to the same message, the conversation thread will be maintained. E-mail programs may offer threaded and unthreaded options. See message thread and thread.