The Message Rewrite Facility (MRF) is a subsystem that is implemented as a series of hooks that allows the administrator to rewrite or discard messages.
Possible uses include:
* marking incoming messages with media from a given account or instance as sensitive
The MRF provides user-configurable policies. The default policy is `NoOpPolicy`, which disables the MRF functionality. Pleroma also includes an easy to use policy called `SimplePolicy` which maps messages matching certain pre-defined criterion to actions built into the policy module.
It is possible to use multiple, active MRF policies at the same time.
## Quarantine Instances
You have the ability to prevent from private / followers-only messages from federating with specific instances. Which means they will only get the public or unlisted messages from your instance.
If, for example, you're using `MIX_ENV=prod` aka using production mode, you would open your configuration file located in `config/prod.secret.exs` and edit or add the option under your `:instance` config object. Then you would specify the instance within quotes.
This example will enable `SimplePolicy`, block media from `illegalporn.biz`, mark media as NSFW from `porn.biz` and `porn.business`, reject messages from `spam.com`, remove messages from `spam.university` from the federated timeline and block reports (flags) from `whiny.whiner`:
The effects of MRF policies can be very drastic. It is important to use this functionality carefully. Always try to talk to an admin before writing an MRF policy concerning their instance.
As discussed above, the MRF system is a modular system that supports pluggable policies. This means that an admin may write a custom MRF policy in Elixir or any other language that runs on the Erlang VM, by specifying the modulename in the `rewrite_policy` config setting.
If you save this file as `lib/pleroma/web/activity_pub/mrf/rewrite_policy.ex`, it will be included when you next rebuild Pleroma. You can enable it in the configuration like so:
Please note that the Pleroma developers consider custom MRF policy modules to fall under the purview of the AGPL. As such, you are obligated to release the sources to your custom MRF policy modules upon request.