A quick bug fix release that affects admins making use of monthly active user limits. You will know if you are affected because 1.9.0 will not start up. Apologies if you were bitten by this one!
Get the new release from github or any of the sources mentioned at https://github.com/matrix-org/synapse/blob/master/INSTALL.md.
Changelog since Synapse 1.9.1
mau_limit_reserved_threepidsconfig would cause Synapse to refuse to start. (#6793)