Email, Messaging, & Video Calls Email Change a Thread's Subject When the Topic Changes Pivot the conversation without losing the thread By Heinz Tschabitscher Writer A former freelance contributor who has reviewed hundreds of email programs and services since 1997. our editorial process Heinz Tschabitscher Updated January 21, 2020 Tim Robberts / Getty Images Email Yahoo! Mail Gmail Tweet Share Email In mailing lists, message boards, and group emails, individual posts often spark lively discussions. As these discussions grow longer, the topic can change substantially. Usually, it has nothing to do anymore with the subject of the original message. You can change the subject header line of a message thread when it becomes apparent that the topic of the discussion has pivoted. Retain the Original Subject Depending on where you are, you may be able to change the subject by typing a new one in the Subject line when writing your reply. But this may not be the best path to take. Rather than change the subject, make it clear that you're continuing an old thread and not starting a new one by including the previous subject line with the new one. If the original subject was "New cloud form discovered," and you want to change it to "The finest English umbrella," the complete new Subject line could be "The finest English umbrella (was: New cloud form discovered)." You can, and probably should shorten the original. If you reply to a message with a (was:) block, remove it. It isn't needed any longer. Caveats When Changing a Subject If you choose to change the subject: Don't edit any of the earlier content or thread messages.Don't remove the recipients of the earlier emails.State why you are changing the subject to avoid confusion. Sometimes Starting Over Is a Better Choice Changing the subject line to start a new conversation can lead to display problems for others and yourself. Email programs and services may lump together the wrong messages in threads. To avoid this problem and the likelihood of being seen as threadjacking, which occurs when someone takes over a thread or email discussion and intentionally posts on a subject unrelated to the original post, create a new message with a new topic instead of starting with a reply.