Email thread replies

A pet peeve of mine: many people do not realize that the email you are replying to is in the email header. (Specifically the “In-Reply-To” and “References” headers)

This feature makes it much easier to thread emails. It is easy for a mail client to tell that message X is in reply to message Y. It also has the side benefit that you can change the subject of a conversation without breaking the thread, if the subject of the conversation changes.

With that said, often people construct a new (non reply) email to a mailing list by

1. Reply to an email sent to the list
2. Clear the subject and contents of the email, and any recipients other than the list itself
3. Set a new subject
4. Write the email

When you do this, your email shows up as a reply to the original email! This is bad — your email might be missed as a reply to an older thread, and you leak information. It clutters up the thread information; neither you nor I want your email nested among the old thread. It makes it harder to read old threads. As such, I go through and manually fix the problem in my mailbox — which means that you’re making me do extra work!

The A correct way to send a new non-reply email to a list

1. Create a new message (not a reply)
2. Set the To: field to the mailing list address
3. Set the subject to whatever
4. Write the email

You can, of course, start with a reply and strip out the relevant headers, if your mail client lets you do that easily.

Note that the converse is also true — it is not correct to construct a reply by creating a new message and copying in the contents of the old one. However, the most common cause of missing reply headers is broken email clients rather than misinformed users.