An email program that consolidates messages with the same subject line so they appear together as a continuous "thread" or "chain." Both email client programs and Web-based email offer threaded email. As long as users reply to the same message, the on-going conversation is maintained as a group. Email programs may offer both threaded and unthreaded options.
Non-Threaded Mail Keeps Duplicating
If email is not threaded, each new reply in a conversation appears in the inbox as a new message. The separate messages make it more cumbersome to review a subject from beginning to end at a later date. See
message thread and
thread.