Email headers (listserv basics part 2)

Email messages are divided into two parts. The body is the main part of the message, and is what most people think of as the message. It is what we discussed earlier when we talked about HTML formatting, for example. The other part contains all the email headers, which are used to describe the message. Like all listserv systems, your groups with uses of these headers to tell you some useful things about the message. Below we explain what all the main email headers are, and how to make the most of them in your group and mailing lists in general.

An email inbox, with the Subject and From email headers

A typical email inbox shows the Subject and From headers.

When you look at your Inbox what you are seeing are the email headers. They describe each email (so they are a type of metadata, or information about data) and allow you to make decisions about what to do with each message. For example, you may decide to file the messages from one group into a folder to read later, while you want to immediately open the messages in a different group that are about the project you are working on currently.

Email headers can be split into two main categories: the headers that you can see, and those that are hidden. Below we describe each of these, before linking off to the technical details for those that are interested.

Email headers that you see

Most of the headers you will see will see are email addresses. However, the Subject is another very important header. The preview text is also very much like header, and we will also discuss that below.


There are a surprisingly large number of addresses . We discuss the four main ones here.


The From-address is the email address of the person that wrote the message, or the author, and it is normally listed in your Inbox. Sending an email to this address will always get to a person. Sometimes rewrites the From address to ensure the email message will get to you, but this address will also get to the author of the email.


The To-address is the intended recipient of the message. This may be a person (such as yourself) or it may be the email address of a group. More than one person, or group, can be listed as the To address.


The CC-address (it stands for carbon copy) lists who else was sent the message. People (or groups) that are listed in the CC are in the loop, but the email is mainly intended for the people listed in the To.


The Reply-to header lists who would like to receive replies. If it is missing replies always go to the From-address. However, your groups with always set a Reply-to, and you can change what it is.


The Subject header describes what an email is about. Like the From address, it is shown in the Inbox and is used by people when they decide if an email should be opened. It is also used by your groups with to determine the topic. You may see some particular things in the Subject.

  • To allow you to see the email messages from your groups they will have the group name at the start, in [square brackets].
  • The letters Re: at the start of a subject show that a message is a reply. To read the messages that came before you can click on the View topic link in the message. (Re stands for the Latin “in re”, or “In the matter of”.)
  • Messages that are sent to someone who decided to then send the email on to you often start with Fwd: or Fw: (for forward).

Preview text

The preview text is shown by some email-programs. Some show it in a pop-up notification, while others show it beneath the Subject. The preview text is shown by the Apple Watch when you get an email, for example. The messages from your groups are written so the preview text lists the number of files, the full name of your group, and the name of your site.

Hidden email headers

There are a lot of email headers, most of which are hidden normally. (Google gives lovely instructions for viewing them if you want to see them all.) Below are some important ones that are set by your groups with


The Sender is the email address of the group that sent the message, as distinct from the author of the message that is listed in the From.


The List-ID is used by email programs to put messages from your group into particular folders. This feature is often called Filter on mailing list, or something similar. (The header looks a little like an email address, but it is not.)


This is the web address of the page for your group.


This is the email address for support, where you can send an email to get help.


This is the address contains the email command to leave a group. Usually if a group member hits the Spam or Junk button in their email program an Unsubscribe message is sent to this address, and the person is removed from the group.

Technical details

There are many standards that govern the Internet, including email. The standards, or Reference for Comment (RFC), are numbered from 1.  The best standard to give you an overview of email is RFC 5598, Internet Mail Architecture. The part most applicable to your group with is Section 5.3, on the headers used by mailing lists.

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