'Server Notices' are a new feature introduced in Synapse 0.30. They provide a channel whereby server administrators can send messages to users on the server.
They are used as part of communication of the server polices (see Consent Tracking), however the intention is that they may also find a use for features such as "Message of the day".
This is a feature specific to Synapse, but it uses standard Matrix communication mechanisms, so should work with any Matrix client.
When the user is first sent a server notice, they will get an invitation to a
room (typically called 'Server Notices', though this is configurable in
homeserver.yaml). They will be unable to reject this invitation -
attempts to do so will receive an error.
Once they accept the invitation, they will see the notice message in the room history; it will appear to have come from the 'server notices user' (see below).
The user is prevented from sending any messages in this room by the power levels.
Having joined the room, the user can leave the room if they want. Subsequent server notices will then cause a new room to be created.
Server notices come from a specific user id on the server. Server
administrators are free to choose the user id - something like
suggested, meaning the notices will come from
@server:<your_server_name>. Once the Server Notices user is configured, that
user id becomes a special, privileged user, so administrators should ensure
that it is not already allocated.
In order to support server notices, it is necessary to add some configuration
homeserver.yaml file. In particular, you should add a
section, which should look like this:
system_mxid_display_name: "Server Notices"
room_name: "Server Notices"
The only compulsory setting is
system_mxid_localpart, which defines the user
id of the Server Notices user, as above.
room_name defines the name of the
room which will be created.
system_mxid_avatar_url can be used to set the
displayname and avatar of the Server Notices user.
To send server notices to users you can use the admin_api.