MSC4373: Server opt-out of specific EDU types

proposals/4373-edu-types.md

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+# MSC4373: Server opt-out of specific EDU types
+
+Some servers may wish to not receive specific types of EDUs, such as presence, to
+cut down on the amount of bandwidth used (as an example).
+
+## Proposal
+
+### `GET /_matrix/federation/v1/edutypes`
+
+This endpoint dictates what types of EDUs the server wishes to receive.
+
+The server should reply with a list of EDU types:
+
+```json
+{
+    "read_receipts": true,
+    "presence": true,
+    "typing": true
+}
+```
+
+Other types of EDUs (signing key updates, device lists, to-device messaging)
+are likely unsafe to opt-out of and thus must not be included.
+
+This endpoint should not require authentication as nothing too sensitive is
+revealed by having it as such.
+
+## Potential issues
+
+Older homeservers (or simply non-compliant ones) will still send unwanted EDUs,
+although these can just be discarded.
+
+## Alternatives
+
+None.
+
+## Security considerations
+
+None.
+
+## Unstable prefix
+
+`/_matrix/federation/unstable/io.fsky.vel/edutypes`
+
+## Dependencies
+
+None.