# Mailing lists service Sympa

**Source**: https://sympa.cms.hu-berlin.de/sympa/help/introduction.html
**Parent**: https://sympa.cms.hu-berlin.de/sympa/help/

## Mailing lists - General introduction

### What is a mailing list?

A mailing list is a **distribution list allowing a group of subscribers to automatically receive by email all messages sent to the list**: every message sent to the list by a subscriber is received by all the other subscribers. When subscribed to a mailing list, it is possible to send messages, to reply to them or to read them without contributing (i.e. to "lurk").

**Special cases:**

- It is sometimes possible to send messages to a mailing list without having subscribed to it. However, you need to be subscribed to a list to receive its messages.
- It is sometimes impossible to send messages to the list even though you are actually subscribed to it: it is the case for announcement lists, which are used to transmit information from a unique sender to a large number of recipients.

### Interest of mailing lists

People subscribe to a mailing list (sometimes abbreviated in ML) to **be informed about a particular topic** and to **take part in exchanges about it**. Examples are:

- mailing list for all the employees of a company;
- mailing list reserved to the participants in a project;
- mailing list dedicated to a class of students;
- mailing list about the latest news in computer security;
- mailing list of mutual aid between handymen;
- mailing list restricted to a family and dedicated to the organization of large family gatherings;
- and so on!

### Types of mailing lists

There are **thousands of mailing lists** of all kinds on the Internet: public or private, free or not, with subscription subject to conditions or not, etc. Those lists may have from a dozen up to several thousand members.

According to the way they work, we can distinguish between **two types of lists**:

- **Announcements lists** allow subscribers to receive messages without being allowed to post some themselves. In fact, those messages are newsletters: electronic magazines, daily services (daily horoscope, daily weather report, daily security alert, etc.), update notices about a website, etc. With this type of mailing list, the information flows from a unique sender to a large number of recipients.
- **Discussion lists** allow all subscribers to take part in exchanges. Those lists can be moderated or not:
  - In a **moderated discussion list**, messages are transmitted to all subscribers after approval by one of the list moderators. Moderation is a token of quality for the list. For example, it ensures that subscribers will not receive off-topic messages, unsolicited commercial messages (spams), messages containing large attachments, etc.
  - In a **non moderated discussion list**, messages are transmitted to all subscribers as soon as the mailing list management robot receives them.

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- [Features](https://sympa.cms.hu-berlin.de/sympa/help/introduction-features.html)
- [How the mailing list service works: roles and responsibilities](https://sympa.cms.hu-berlin.de/sympa/help/introduction-roles.html)
- [Regulatory framework](https://sympa.cms.hu-berlin.de/sympa/help/introduction-policy.html)