config_documentation.md

# Configuring Synapse

This is intended as a guide to the Synapse configuration. The behavior of a Synapse instance can be modified 
through the many configuration settings documented here — each config option is explained, 
including what the default is, how to change the default and what sort of behaviour the setting governs.
Also included is an example configuration for each setting. If you don't want to spend a lot of time 
thinking about options, the config as generated sets sensible defaults for all values. Do note however that the
database defaults to SQLite, which is not recommended for production usage. You can read more on this subject 
[here](../../setup/installation.md#using-postgresql).

## Config Conventions

Configuration options that take a time period can be set using a number
followed by a letter. Letters have the following meanings:

* `s` = second
* `m` = minute
* `h` = hour
* `d` = day
* `w` = week
* `y` = year

For example, setting `redaction_retention_period: 5m` would remove redacted
messages from the database after 5 minutes, rather than 5 months.

In addition, configuration options referring to size use the following suffixes:

* `M` = MiB, or 1,048,576 bytes
* `K` = KiB, or 1024 bytes 

For example, setting `max_avatar_size: 10M` means that Synapse will not accept files larger than 10,485,760 bytes
for a user avatar. 

### YAML 
The configuration file is a [YAML](https://yaml.org/) file, which means that certain syntax rules
apply if you want your config file to be read properly. A few helpful things to know:
* `#` before any option in the config will comment out that setting and either a default (if available) will 
   be applied or Synapse will ignore the setting. Thus, in example #1 below, the setting will be read and
   applied, but in example #2 the setting will not be read and a default will be applied.  

   Example #1:
   ```yaml
   pid_file: DATADIR/homeserver.pid
   ```
   Example #2:
   ```yaml
   #pid_file: DATADIR/homeserver.pid
   ```
* Indentation matters! The indentation before a setting
  will determine whether a given setting is read as part of another
  setting, or considered on its own. Thus, in example #1, the `enabled` setting
  is read as a sub-option of the `presence` setting, and will be properly applied.
  
  However, the lack of indentation before the `enabled` setting in example #2 means
  that when reading the config, Synapse will consider both `presence` and `enabled` as
  different settings. In this case, `presence` has no value, and thus a default applied, and `enabled`
  is an option that Synapse doesn't recognize and thus ignores.
  
  Example #1: 
  ```yaml
  presence:
    enabled: false
  ```
  Example #2:
  ```yaml
  presence:
  enabled: false
  ```
  In this manual, all top-level settings (ones with no indentation) are identified 
  at the beginning of their section (i.e. "### `example_setting`") and 
  the sub-options, if any, are identified and listed in the body of the section. 
  In addition, each setting has an example of its usage, with the proper indentation
  shown. 

## Contents
[Modules](#modules)

[Server](#server)

[Homeserver Blocking](#homeserver-blocking)

[TLS](#tls)

[Federation](#federation)

[Caching](#caching)

[Database](#database)

[Logging](#logging)

[Ratelimiting](#ratelimiting)

[Media Store](#media-store)

[Captcha](#captcha)

[TURN](#turn)

[Registration](#registration)

[API Configuration](#api-configuration)

[Signing Keys](#signing-keys)

[Single Sign On Integration](#single-sign-on-integration)

[Push](#push)

[Rooms](#rooms)

[Opentracing](#opentracing)

[Workers](#workers)

[Background Updates](#background-updates)

## Modules

Server admins can expand Synapse's functionality with external modules.

See [here](../../modules/index.md) for more
documentation on how to configure or create custom modules for Synapse.


---
### `modules`

Use the `module` sub-option to add modules under this option to extend functionality. 
The `module` setting then has a sub-option, `config`, which can be used to define some configuration
for the `module`.

Defaults to none.

Example configuration:
```yaml
modules:
  - module: my_super_module.MySuperClass
    config:
      do_thing: true
  - module: my_other_super_module.SomeClass
    config: {}
```
---
## Server ##

Define your homeserver name and other base options.

---
### `server_name`

This sets the public-facing domain of the server.

The `server_name` name will appear at the end of usernames and room addresses
created on your server. For example if the `server_name` was example.com,
usernames on your server would be in the format `@user:example.com`

In most cases you should avoid using a matrix specific subdomain such as
matrix.example.com or synapse.example.com as the `server_name` for the same
reasons you wouldn't use user@email.example.com as your email address.
See [here](../../delegate.md)
for information on how to host Synapse on a subdomain while preserving
a clean `server_name`.

The `server_name` cannot be changed later so it is important to
configure this correctly before you start Synapse. It should be all
lowercase and may contain an explicit port.

There is no default for this option. 
 
Example configuration #1:
```yaml
server_name: matrix.org 
```
Example configuration #2:
```yaml
server_name: localhost:8080
```
---
### `pid_file`

When running Synapse as a daemon, the file to store the pid in. Defaults to none.

Example configuration:
```yaml
pid_file: DATADIR/homeserver.pid
```
---
### `web_client_location`

The absolute URL to the web client which `/` will redirect to. Defaults to none. 

Example configuration:
```yaml
web_client_location: https://riot.example.com/
```
---
### `public_baseurl`

The public-facing base URL that clients use to access this Homeserver (not
including _matrix/...). This is the same URL a user might enter into the
'Custom Homeserver URL' field on their client. If you use Synapse with a
reverse proxy, this should be the URL to reach Synapse via the proxy.
Otherwise, it should be the URL to reach Synapse's client HTTP listener (see
'listeners' below).

Defaults to `https://<server_name>/`.

Example configuration:
```yaml
public_baseurl: https://example.com/
```
---
### `serve_server_wellknown`

By default, other servers will try to reach our server on port 8448, which can
be inconvenient in some environments.

Provided `https://<server_name>/` on port 443 is routed to Synapse, this
option configures Synapse to serve a file at `https://<server_name>/.well-known/matrix/server`. 
This will tell other servers to send traffic to port 443 instead.

This option currently defaults to false.

See https://matrix-org.github.io/synapse/latest/delegate.html for more
information.

Example configuration:
```yaml
serve_server_wellknown: true
```
---
### `extra_well_known_client_content `

This option allows server runners to add arbitrary key-value pairs to the [client-facing `.well-known` response](https://spec.matrix.org/latest/client-server-api/#well-known-uri).
Note that the `public_baseurl` config option must be provided for Synapse to serve a response to `/.well-known/matrix/client` at all.

If this option is provided, it parses the given yaml to json and 
serves it on `/.well-known/matrix/client` endpoint
alongside the standard properties.

Example configuration:
```yaml
extra_well_known_client_content : 
  option1: value1
  option2: value2
```
---
### `soft_file_limit`
 
Set the soft limit on the number of file descriptors synapse can use.
Zero is used to indicate synapse should set the soft limit to the hard limit.
Defaults to 0. 

Example configuration:
```yaml
soft_file_limit: 3
```
---
### `presence`

Presence tracking allows users to see the state (e.g online/offline)
of other local and remote users. Set the `enabled` sub-option to false to  
disable presence tracking on this homeserver. Defaults to true. 
This option replaces the previous top-level 'use_presence' option.

Example configuration:
```yaml
presence:
  enabled: false
```
---
### `require_auth_for_profile_requests`

Whether to require authentication to retrieve profile data (avatars, display names) of other 
users through the client API. Defaults to false. Note that profile data is also available 
via the federation API, unless `allow_profile_lookup_over_federation` is set to false.

Example configuration:
```yaml
require_auth_for_profile_requests: true
```
---
### `limit_profile_requests_to_users_who_share_rooms`

Use this option to require a user to share a room with another user in order
to retrieve their profile information. Only checked on Client-Server 
requests. Profile requests from other servers should be checked by the
requesting server. Defaults to false.

Example configuration: 
```yaml
limit_profile_requests_to_users_who_share_rooms: true
```
---
### `include_profile_data_on_invite`

Use this option to prevent a user's profile data from being retrieved and
displayed in a room until they have joined it. By default, a user's
profile data is included in an invite event, regardless of the values
of the above two settings, and whether or not the users share a server.
Defaults to true.

Example configuration:
```yaml
include_profile_data_on_invite: false
```
---
### `allow_public_rooms_without_auth`

If set to true, removes the need for authentication to access the server's
public rooms directory through the client API, meaning that anyone can
query the room directory. Defaults to false.

Example configuration:
```yaml
allow_public_rooms_without_auth: true
```
---
### `allow_public_rooms_over_federation`

If set to true, allows any other homeserver to fetch the server's public
rooms directory via federation. Defaults to false.

Example configuration:
```yaml
allow_public_rooms_over_federation: true
```
---
### `default_room_version`

The default room version for newly created rooms on this server.

Known room versions are listed [here](https://spec.matrix.org/latest/rooms/#complete-list-of-room-versions)

For example, for room version 1, `default_room_version` should be set
to "1". 

Currently defaults to "9".

Example configuration:
```yaml
default_room_version: "8"
```
---
### `gc_thresholds`

The garbage collection threshold parameters to pass to `gc.set_threshold`, if defined.
Defaults to none. 

Example configuration:
```yaml
gc_thresholds: [700, 10, 10]
```
---
### `gc_min_interval`

The minimum time in seconds between each GC for a generation, regardless of
the GC thresholds. This ensures that we don't do GC too frequently. A value of `[1s, 10s, 30s]` 
indicates that a second must pass between consecutive generation 0 GCs, etc.

Defaults to `[1s, 10s, 30s]`.

Example configuration:
```yaml
gc_min_interval: [0.5s, 30s, 1m]
```
---
### `filter_timeline_limit`

Set the limit on the returned events in the timeline in the get
and sync operations. Defaults to 100. A value of -1 means no upper limit.


Example configuration:
```yaml
filter_timeline_limit: 5000
```
---
### `block_non_admin_invites`

Whether room invites to users on this server should be blocked
(except those sent by local server admins). Defaults to false.

Example configuration:
```yaml
block_non_admin_invites: true
```
---
### `enable_search`

If set to false, new messages will not be indexed for searching and users
will receive errors when searching for messages. Defaults to true.

Example configuration:
```yaml
enable_search: false
```
---
### `ip_range_blacklist`
 
This option prevents outgoing requests from being sent to the specified blacklisted IP address
CIDR ranges. If this option is not specified then it defaults to private IP
address ranges (see the example below).

The blacklist applies to the outbound requests for federation, identity servers,
push servers, and for checking key validity for third-party invite events.

(0.0.0.0 and :: are always blacklisted, whether or not they are explicitly
listed here, since they correspond to unroutable addresses.)

This option replaces `federation_ip_range_blacklist` in Synapse v1.25.0.

Note: The value is ignored when an HTTP proxy is in use.

Example configuration:
```yaml
ip_range_blacklist:
  - '127.0.0.0/8'
  - '10.0.0.0/8'
  - '172.16.0.0/12'
  - '192.168.0.0/16'
  - '100.64.0.0/10'
  - '192.0.0.0/24'
  - '169.254.0.0/16'
  - '192.88.99.0/24'
  - '198.18.0.0/15'
  - '192.0.2.0/24'
  - '198.51.100.0/24'
  - '203.0.113.0/24'
  - '224.0.0.0/4'
  - '::1/128'
  - 'fe80::/10'
  - 'fc00::/7'
  - '2001:db8::/32'
  - 'ff00::/8'
  - 'fec0::/10'
```
---
### `ip_range_whitelist`

List of IP address CIDR ranges that should be allowed for federation,
identity servers, push servers, and for checking key validity for
third-party invite events. This is useful for specifying exceptions to
wide-ranging blacklisted target IP ranges - e.g. for communication with
a push server only visible in your network.

This whitelist overrides `ip_range_blacklist` and defaults to an empty
list.

Example configuration:
```yaml
ip_range_whitelist:
   - '192.168.1.1'
```
---
### `listeners`

List of ports that Synapse should listen on, their purpose and their
configuration.

Sub-options for each listener include:

* `port`: the TCP port to bind to. 

* `bind_addresses`: a list of local addresses to listen on. The default is
       'all local interfaces'.

* `type`: the type of listener. Normally `http`, but other valid options are:
    
   * `manhole`: (see the docs [here](../../manhole.md)),

   * `metrics`: (see the docs [here](../../metrics-howto.md)),

   * `replication`: (see the docs [here](../../workers.md)).

* `tls`: set to true to enable TLS for this listener. Will use the TLS key/cert specified in tls_private_key_path / tls_certificate_path.

* `x_forwarded`: Only valid for an 'http' listener. Set to true to use the X-Forwarded-For header as the client IP. Useful when Synapse is
   behind a reverse-proxy.

* `resources`: Only valid for an 'http' listener. A list of resources to host
   on this port. Sub-options for each resource are:

   * `names`: a list of names of HTTP resources. See below for a list of valid resource names.

   * `compress`: set to true to enable HTTP compression for this resource.

* `additional_resources`: Only valid for an 'http' listener. A map of
   additional endpoints which should be loaded via dynamic modules.

Valid resource names are:

* `client`: the client-server API (/_matrix/client), and the synapse admin API (/_synapse/admin). Also implies `media` and `static`.

* `consent`: user consent forms (/_matrix/consent). See [here](../../consent_tracking.md) for more.

* `federation`: the server-server API (/_matrix/federation). Also implies `media`, `keys`, `openid`

* `keys`: the key discovery API (/_matrix/key).

* `media`: the media API (/_matrix/media).

* `metrics`: the metrics interface. See [here](../../metrics-howto.md).

* `openid`: OpenID authentication. See [here](../../openid.md).

* `replication`: the HTTP replication API (/_synapse/replication). See [here](../../workers.md).

* `static`: static resources under synapse/static (/_matrix/static). (Mostly useful for 'fallback authentication'.)

Example configuration #1:
```yaml
listeners:
  # TLS-enabled listener: for when matrix traffic is sent directly to synapse.
  #
  # (Note that you will also need to give Synapse a TLS key and certificate: see the TLS section
  # below.)
  #
  - port: 8448
    type: http
    tls: true
    resources:
      - names: [client, federation]
```
Example configuration #2:
```yaml
listeners:
  # Unsecure HTTP listener: for when matrix traffic passes through a reverse proxy
  # that unwraps TLS.
  #
  # If you plan to use a reverse proxy, please see
  # https://matrix-org.github.io/synapse/latest/reverse_proxy.html.
  #
  - port: 8008
    tls: false
    type: http
    x_forwarded: true
    bind_addresses: ['::1', '127.0.0.1']

    resources:
      - names: [client, federation]
        compress: false

    # example additional_resources:
    additional_resources:
      "/_matrix/my/custom/endpoint":
        module: my_module.CustomRequestHandler
        config: {}

  # Turn on the twisted ssh manhole service on localhost on the given
  # port.
  - port: 9000
    bind_addresses: ['::1', '127.0.0.1']
    type: manhole
```
---
### `manhole_settings`

Connection settings for the manhole. You can find more information
on the manhole [here](../../manhole.md). Manhole sub-options include:
* `username` : the username for the manhole. This defaults to 'matrix'.
* `password`: The password for the manhole. This defaults to 'rabbithole'.
* `ssh_priv_key_path` and `ssh_pub_key_path`: The private and public SSH key pair used to encrypt the manhole traffic.
  If these are left unset, then hardcoded and non-secret keys are used,
  which could allow traffic to be intercepted if sent over a public network.

Example configuration:
```yaml
manhole_settings:
  username: manhole
  password: mypassword
  ssh_priv_key_path: CONFDIR/id_rsa
  ssh_pub_key_path: CONFDIR/id_rsa.pub
```
---
### `dummy_events_threshold`

Forward extremities can build up in a room due to networking delays between
homeservers. Once this happens in a large room, calculation of the state of
that room can become quite expensive. To mitigate this, once the number of
forward extremities reaches a given threshold, Synapse will send an
`org.matrix.dummy_event` event, which will reduce the forward extremities
in the room.

This setting defines the threshold (i.e. number of forward extremities in the room) at which dummy events are sent. 
The default value is 10.

Example configuration:
```yaml
dummy_events_threshold: 5
```
---
### `delete_stale_devices_after`

An optional duration. If set, Synapse will run a daily background task to log out and
delete any device that hasn't been accessed for more than the specified amount of time.

Defaults to no duration, which means devices are never pruned.

Example configuration:
```yaml
delete_stale_devices_after: 1y
```

## Homeserver blocking ##
Useful options for Synapse admins.

---

### `admin_contact`

How to reach the server admin, used in `ResourceLimitError`. Defaults to none. 

Example configuration:
```yaml
admin_contact: 'mailto:admin@server.com'
```
---
### `hs_disabled` and `hs_disabled_message`

Blocks users from connecting to the homeserver and provides a human-readable reason
why the connection was blocked. Defaults to false. 

Example configuration:
```yaml
hs_disabled: true
hs_disabled_message: 'Reason for why the HS is blocked'
```
---
### `limit_usage_by_mau`

This option disables/enables monthly active user blocking. Used in cases where the admin or 
server owner wants to limit to the number of monthly active users. When enabled and a limit is 
reached the server returns a `ResourceLimitError` with error type `Codes.RESOURCE_LIMIT_EXCEEDED`.
Defaults to false. If this is enabled, a value for `max_mau_value` must also be set.

Example configuration:
```yaml
limit_usage_by_mau: true 
```
---
### `max_mau_value`

This option sets the hard limit of monthly active users above which the server will start 
blocking user actions if `limit_usage_by_mau` is enabled. Defaults to 0.  

Example configuration:
```yaml
max_mau_value: 50
```
---
### `mau_trial_days`

The option `mau_trial_days` is a means to add a grace period for active users. It
means that users must be active for the specified number of days before they
can be considered active and guards against the case where lots of users
sign up in a short space of time never to return after their initial
session. Defaults to 0. 

Example configuration:
```yaml
mau_trial_days: 5
```
---
### `mau_appservice_trial_days`

The option `mau_appservice_trial_days` is similar to `mau_trial_days`, but applies a different
trial number if the user was registered by an appservice. A value
of 0 means no trial days are applied. Appservices not listed in this dictionary
use the value of `mau_trial_days` instead.

Example configuration:
```yaml
mau_appservice_trial_days: 
  my_appservice_id: 3
  another_appservice_id: 6
```
---
### `mau_limit_alerting`

The option `mau_limit_alerting` is a means of limiting client-side alerting
should the mau limit be reached. This is useful for small instances
where the admin has 5 mau seats (say) for 5 specific people and no
interest increasing the mau limit further. Defaults to true, which
means that alerting is enabled.

Example configuration:
```yaml
mau_limit_alerting: false
```
---
### `mau_stats_only`

If enabled, the metrics for the number of monthly active users will
be populated, however no one will be limited based on these numbers. If `limit_usage_by_mau`
is true, this is implied to be true. Defaults to false. 

Example configuration:
```yaml
mau_stats_only: true
```
---
### `mau_limit_reserved_threepids`

Sometimes the server admin will want to ensure certain accounts are
never blocked by mau checking. These accounts are specified by this option.
Defaults to none. Add accounts by specifying the `medium` and `address` of the
reserved threepid (3rd party identifier).

Example configuration:
```yaml
mau_limit_reserved_threepids:
  - medium: 'email'
    address: 'reserved_user@example.com'
```
---
### `server_context`

This option is used by phonehome stats to group together related servers.
Defaults to none. 

Example configuration:
```yaml
server_context: context
```
---
### `limit_remote_rooms`

When this option is enabled, the room "complexity" will be checked before a user
joins a new remote room. If it is above the complexity limit, the server will
disallow joining, or will instantly leave. This is useful for homeservers that are
resource-constrained. Options for this setting include:
* `enabled`: whether this check is enabled. Defaults to false.
* `complexity`: the limit above which rooms cannot be joined. The default is 1.0.
* `complexity_error`: override the error which is returned when the room is too complex with a
   custom message. 
* `admins_can_join`: allow server admins to join complex rooms. Default is false.

Room complexity is an arbitrary measure based on factors such as the number of
users in the room. 

Example configuration:
```yaml
limit_remote_rooms:
  enabled: true
  complexity: 0.5
  complexity_error: "I can't let you do that, Dave."
  admins_can_join: true
```
---
### `require_membership_for_aliases`

Whether to require a user to be in the room to add an alias to it.
Defaults to true.

Example configuration:
```yaml
require_membership_for_aliases: false
```
---
### `allow_per_room_profiles`

Whether to allow per-room membership profiles through the sending of membership
events with profile information that differs from the target's global profile.
Defaults to true.

Example configuration:
```yaml
allow_per_room_profiles: false
```
---
### `max_avatar_size`

The largest permissible file size in bytes for a user avatar. Defaults to no restriction.
Use M for MB and K for KB. 

Note that user avatar changes will not work if this is set without using Synapse's media repository.

Example configuration:
```yaml
max_avatar_size: 10M
```
---
### `allowed_avatar_mimetypes`

The MIME types allowed for user avatars. Defaults to no restriction.

Note that user avatar changes will not work if this is set without
using Synapse's media repository.

Example configuration:
```yaml
allowed_avatar_mimetypes: ["image/png", "image/jpeg", "image/gif"]
```
---
### `redaction_retention_period`

How long to keep redacted events in unredacted form in the database. After
this period redacted events get replaced with their redacted form in the DB.

Defaults to `7d`. Set to `null` to disable.

Example configuration:
```yaml
redaction_retention_period: 28d
```
---
### `user_ips_max_age` 

How long to track users' last seen time and IPs in the database.

Defaults to `28d`. Set to `null` to disable clearing out of old rows.

Example configuration:
```yaml
user_ips_max_age: 14d
```
---
### `request_token_inhibit_3pid_errors`

Inhibits the `/requestToken` endpoints from returning an error that might leak
information about whether an e-mail address is in use or not on this
homeserver. Defaults to false. 
Note that for some endpoints the error situation is the e-mail already being
used, and for others the error is entering the e-mail being unused.
If this option is enabled, instead of returning an error, these endpoints will
act as if no error happened and return a fake session ID ('sid') to clients.

Example configuration:
```yaml
request_token_inhibit_3pid_errors: true
```
---
### `next_link_domain_whitelist`

A list of domains that the domain portion of `next_link` parameters
must match.

This parameter is optionally provided by clients while requesting
validation of an email or phone number, and maps to a link that
users will be automatically redirected to after validation
succeeds. Clients can make use this parameter to aid the validation
process.

The whitelist is applied whether the homeserver or an identity server is handling validation.

The default value is no whitelist functionality; all domains are
allowed. Setting this value to an empty list will instead disallow
all domains.

Example configuration:
```yaml
next_link_domain_whitelist: ["matrix.org"]
```
---
### `templates` and `custom_template_directory`

These options define templates to use when generating email or HTML page contents.
The `custom_template_directory` determines which directory Synapse will try to 
find template files in to use to generate email or HTML page contents.
If not set, or a file is not found within the template directory, a default 
template from within the Synapse package will be used.

See [here](../../templates.md) for more
information about using custom templates.

Example configuration:
```yaml
templates:
  custom_template_directory: /path/to/custom/templates/
```
---
### `retention`

This option and the associated options determine message retention policy at the
server level.

Room admins and mods can define a retention period for their rooms using the
`m.room.retention` state event, and server admins can cap this period by setting
the `allowed_lifetime_min` and `allowed_lifetime_max` config options.

If this feature is enabled, Synapse will regularly look for and purge events
which are older than the room's maximum retention period. Synapse will also
filter events received over federation so that events that should have been 
purged are ignored and not stored again. 

The message retention policies feature is disabled by default.

This setting has the following sub-options:
* `default_policy`: Default retention policy. If set, Synapse will apply it to rooms that lack the
   'm.room.retention' state event. This option is further specified by the 
   `min_lifetime` and `max_lifetime` sub-options associated with it. Note that the 
    value of `min_lifetime` doesn't matter much because Synapse doesn't take it into account yet. 

* `allowed_lifetime_min` and `allowed_lifetime_max`: Retention policy limits. If 
   set, and the state of a room contains a `m.room.retention` event in its state 
   which contains a `min_lifetime` or a `max_lifetime` that's out of these bounds,
   Synapse will cap the room's policy to these limits when running purge jobs.

* `purge_jobs` and the associated `shortest_max_lifetime` and `longest_max_lifetime` sub-options:
   Server admins can define the settings of the background jobs purging the
   events whose lifetime has expired under the `purge_jobs` section.
   
  If no configuration is provided for this option, a single job will be set up to delete
  expired events in every room daily.

  Each job's configuration defines which range of message lifetimes the job
  takes care of. For example, if `shortest_max_lifetime` is '2d' and
  `longest_max_lifetime` is '3d', the job will handle purging expired events in
  rooms whose state defines a `max_lifetime` that's both higher than 2 days, and
  lower than or equal to 3 days. Both the minimum and the maximum value of a
  range are optional, e.g. a job with no `shortest_max_lifetime` and a
  `longest_max_lifetime` of '3d' will handle every room with a retention policy
  whose `max_lifetime` is lower than or equal to three days.
  
  The rationale for this per-job configuration is that some rooms might have a
  retention policy with a low `max_lifetime`, where history needs to be purged
  of outdated messages on a more frequent basis than for the rest of the rooms
  (e.g. every 12h), but not want that purge to be performed by a job that's
  iterating over every room it knows, which could be heavy on the server.

  If any purge job is configured, it is strongly recommended to have at least
  a single job with neither `shortest_max_lifetime` nor `longest_max_lifetime`
  set, or one job without `shortest_max_lifetime` and one job without
  `longest_max_lifetime` set. Otherwise some rooms might be ignored, even if
  `allowed_lifetime_min` and `allowed_lifetime_max` are set, because capping a
  room's policy to these values is done after the policies are retrieved from
  Synapse's database (which is done using the range specified in a purge job's
  configuration).

Example configuration:
```yaml
retention:
  enabled: true
  default_policy:
    min_lifetime: 1d
    max_lifetime: 1y
  allowed_lifetime_min: 1d
  allowed_lifetime_max: 1y
  purge_jobs:
    - longest_max_lifetime: 3d
      interval: 12h
    - shortest_max_lifetime: 3d
      interval: 1d  
```
---
## TLS ##

Options related to TLS.

---
### `tls_certificate_path`

This option specifies a PEM-encoded X509 certificate for TLS.
This certificate, as of Synapse 1.0, will need to be a valid and verifiable
certificate, signed by a recognised Certificate Authority. Defaults to none. 

Be sure to use a `.pem` file that includes the full certificate chain including
any intermediate certificates (for instance, if using certbot, use
`fullchain.pem` as your certificate, not `cert.pem`). 

Example configuration:
```yaml
tls_certificate_path: "CONFDIR/SERVERNAME.tls.crt"
```
---
### `tls_private_key_path`

PEM-encoded private key for TLS. Defaults to none. 

Example configuration:
```yaml
tls_private_key_path: "CONFDIR/SERVERNAME.tls.key"
```
---
### `federation_verify_certificates`
Whether to verify TLS server certificates for outbound federation requests.

Defaults to true. To disable certificate verification, set the option to false.

Example configuration:
```yaml
federation_verify_certificates: false
```
---
### `federation_client_minimum_tls_version`

The minimum TLS version that will be used for outbound federation requests.

Defaults to `1`. Configurable to `1`, `1.1`, `1.2`, or `1.3`. Note
that setting this value higher than `1.2` will prevent federation to most
of the public Matrix network: only configure it to `1.3` if you have an
entirely private federation setup and you can ensure TLS 1.3 support.

Example configuration:
```yaml
federation_client_minimum_tls_version: 1.2
```
---