- Special-case a support user for use in verifying behaviour of a given server. The support user does not appear in user directory or monthly active user counts. ([\#4141](https://github.com/matrix-org/synapse/issues/4141))
- Support for serving .well-known files ([\#4262](https://github.com/matrix-org/synapse/issues/4262))
- SAML2 authentication: Initialise user display name from SAML2 data ([\#4272](https://github.com/matrix-org/synapse/issues/4272))
- Synapse can now have its conditional/extra dependencies installed by pip. This functionality can be used by using `pip install matrix-synapse[feature]`, where feature is a comma separated list with the possible values "email.enable_notifs", "ldap3", "postgres", "saml2", "url_preview", and "test". If you want to install all optional dependencies, you can use "all" instead. ([\#4298](https://github.com/matrix-org/synapse/issues/4298), [\#4325](https://github.com/matrix-org/synapse/issues/4325))
- Add routes for reading account data. ([\#4303](https://github.com/matrix-org/synapse/issues/4303))
- Add opt-in support for v2 rooms ([\#4307](https://github.com/matrix-org/synapse/issues/4307))
- Add a script to generate a clean config file ([\#4315](https://github.com/matrix-org/synapse/issues/4315))
- Return server data in /login response ([\#4319](https://github.com/matrix-org/synapse/issues/4319))
Bugfixes
--------
- Fix contains_url check to be consistent with other instances in code-base and check that value is an instance of string. ([\#3405](https://github.com/matrix-org/synapse/issues/3405))
- Fix CAS login when username is not valid in an MXID ([\#4264](https://github.com/matrix-org/synapse/issues/4264))
- Send CORS headers for /media/config ([\#4279](https://github.com/matrix-org/synapse/issues/4279))
- Add 'sandbox' to CSP for media reprository ([\#4284](https://github.com/matrix-org/synapse/issues/4284))
- Make the new landing page prettier. ([\#4294](https://github.com/matrix-org/synapse/issues/4294))
- Fix deleting E2E room keys when using old SQLite versions. ([\#4295](https://github.com/matrix-org/synapse/issues/4295))
- The metric synapse_admin_mau:current previously did not update when config.mau_stats_only was set to True ([\#4305](https://github.com/matrix-org/synapse/issues/4305))
- Fixed per-room account data filters ([\#4309](https://github.com/matrix-org/synapse/issues/4309))
- Fix indentation in default config ([\#4313](https://github.com/matrix-org/synapse/issues/4313))
- Fix test_metric.py compatibility with prometheus_client 0.5. Contributed by Maarten de Vries <maarten@de-vri.es>. ([\#4317](https://github.com/matrix-org/synapse/issues/4317))
- Avoid packaging _trial_temp directory in -py3 debian packages ([\#4326](https://github.com/matrix-org/synapse/issues/4326))
- Check jinja version for consent resource ([\#4327](https://github.com/matrix-org/synapse/issues/4327))
- fix NPE in /messages by checking if all events were filtered out ([\#4330](https://github.com/matrix-org/synapse/issues/4330))
- Fix synchrotron exploding due to being unable to access is_support_user in storage layer ([\#4344](https://github.com/matrix-org/synapse/issues/4344))
- Fix `python -m synapse.config` on Python 3. ([\#4356](https://github.com/matrix-org/synapse/issues/4356))
Deprecations and Removals
-------------------------
- Remove the deprecated v1/register API on Python 2. It was never ported to Python 3. ([\#4334](https://github.com/matrix-org/synapse/issues/4334))
Internal Changes
----------------
- Getting URL previews of IP addresses no longer fails on Python 3. ([\#4215](https://github.com/matrix-org/synapse/issues/4215))
- drop undocumented dependency on dateutil ([\#4266](https://github.com/matrix-org/synapse/issues/4266))
- Update the example systemd config to use a virtualenv ([\#4273](https://github.com/matrix-org/synapse/issues/4273))
- Update link to kernel DCO guide ([\#4274](https://github.com/matrix-org/synapse/issues/4274))
- Make isort tox check print diff when it fails ([\#4283](https://github.com/matrix-org/synapse/issues/4283))
- Log room_id in Unknown room errors ([\#4297](https://github.com/matrix-org/synapse/issues/4297))
- Documentation improvements for coturn setup. Contributed by Krithin Sitaram. ([\#4333](https://github.com/matrix-org/synapse/issues/4333))
- Update pull request template to use absolute links ([\#4341](https://github.com/matrix-org/synapse/issues/4341))
- Update README to not lie about required restart when updating TLS certificates ([\#4343](https://github.com/matrix-org/synapse/issues/4343))
- Update debian packaging for compatibility with transitional package ([\#4349](https://github.com/matrix-org/synapse/issues/4349))
- Fix command hint to generate a config file when trying to start without a config file ([\#4353](https://github.com/matrix-org/synapse/issues/4353))
- Add better logging for unexpected errors while sending transactions ([\#4358](https://github.com/matrix-org/synapse/issues/4358))