# Aliases

> [!WARNING]
> This is a design document and does not necessarily reflect the current state
> of the implementation.

[Mail aliases](https://en.wikipedia.org/wiki/Email_alias) are supported in llldap, in three forms:

- *user aliases* are associated with an account, in order to provide more pseudonymity and limit
  damage in case of data breach (eg. signup to Google with `mygooglealias@example.com`)
- *group aliases* are a simple group with special permission to receive emails; all emails
  are forwarded to all members, and all members can send mail from the alias
- *service aliases* are reserved keywords (eg. `abuse`) on every domain and forward emails they receive
  both to domain admins and to global admins

## User aliases

Depending on a domain's configuration, a user may or may not create aliases. When a user acquires an
alias, it is associated to their account forever.

When deleted, your alias remains as a *tombstone* preventing another user from acquiring it and receiving your mail.
An alias can be recovered (re-enabled) by its owner at any time. Email to a deleted alias just doesn't go anywhere.

**TODO:** Maybe we'd like domain admins to be able to reclaim tombstones?

## Group aliases

A group on a domain may or may not be configured as a mail alias. When it is, all group members can send and
receive mail with the group's address, such as `mygroup@example.com`.

As a consequence, `uid` on a domain are unique across users and groups. If there is already a user account
`example@example.com`, then we cannot create a group `example@example.com`.

A deleted group remains as a *tombstone* to prevent leaking future group emails by a new user registering
as the group name. Email to a deleted group, or to a group that has disabled email, just doesn't go anywhere.

**TODO:** Maybe we'd like domain admins to be able to reclaim tombstones?

## Service aliases

Some special keywords are reserved for important mail communication: *admin*, *admins*, *root*, *hostmaster*, *postmaster*, *abuse*.
**TODO:** should `contact@` be in this list as well?

The `admins` group on each domain can be edited by domain admins to add/remove admins for the domain.
All global admins are part of every domain's `admins` group, and a domain admin cannot remove them.
Others are meta-groups that cannot ever be edited, and refer to the domain's `admins` group for membership information.

# TODO

If we support a group as mailalias, how do we prevent collisions between users and groups?

- [ ] User aliases in DB
- [ ] Aliases in LDAP search responses
- [ ] Domain config to allow/disallow user aliases on domain
- [ ] Group setting to enable/disable receiving email to this group