diff --git a/crates/handlers/src/graphql/mutations/user_email.rs b/crates/handlers/src/graphql/mutations/user_email.rs
index 4a0c51853..19ff39804 100644
--- a/crates/handlers/src/graphql/mutations/user_email.rs
+++ b/crates/handlers/src/graphql/mutations/user_email.rs
@@ -398,6 +398,7 @@ impl UserEmailMutations {
         let state = ctx.state();
         let id = NodeType::User.extract_ulid(&input.user_id)?;
         let requester = ctx.requester();
+        let requester_fingerprint = ctx.requester_fingerprint();
         let clock = state.clock();
         let mut rng = state.rng();
 
@@ -427,6 +428,7 @@ impl UserEmailMutations {
             let res = policy
                 .evaluate_email(mas_policy::EmailInput {
                     email: &input.email,
+                    requester: requester_fingerprint.into(),
                 })
                 .await?;
             if !res.valid() {
@@ -559,6 +561,7 @@ impl UserEmailMutations {
         let mut rng = state.rng();
         let clock = state.clock();
         let requester = ctx.requester();
+        let requester_fingerprint = ctx.requester_fingerprint();
         let limiter = state.limiter();
 
         // Only allow calling this if the requester is a browser session
@@ -617,6 +620,7 @@ impl UserEmailMutations {
         let res = policy
             .evaluate_email(mas_policy::EmailInput {
                 email: &input.email,
+                requester: requester_fingerprint.into(),
             })
             .await?;
         if !res.valid() {
diff --git a/crates/handlers/src/oauth2/authorization/complete.rs b/crates/handlers/src/oauth2/authorization/complete.rs
index ba2786240..205809c19 100644
--- a/crates/handlers/src/oauth2/authorization/complete.rs
+++ b/crates/handlers/src/oauth2/authorization/complete.rs
@@ -231,6 +231,9 @@ pub(crate) async fn complete(
             client,
             scope: &grant.scope,
             grant_type: mas_policy::GrantType::AuthorizationCode,
+            requester: mas_policy::Requester {
+                ip_address: activity_tracker.ip(),
+            },
         })
         .await?;
 
diff --git a/crates/handlers/src/oauth2/consent.rs b/crates/handlers/src/oauth2/consent.rs
index b2b99b372..b549eaff5 100644
--- a/crates/handlers/src/oauth2/consent.rs
+++ b/crates/handlers/src/oauth2/consent.rs
@@ -116,6 +116,9 @@ pub(crate) async fn get(
                 client: &client,
                 scope: &grant.scope,
                 grant_type: mas_policy::GrantType::AuthorizationCode,
+                requester: mas_policy::Requester {
+                    ip_address: activity_tracker.ip(),
+                },
             })
             .await?;
 
@@ -195,6 +198,9 @@ pub(crate) async fn post(
             client: &client,
             scope: &grant.scope,
             grant_type: mas_policy::GrantType::AuthorizationCode,
+            requester: mas_policy::Requester {
+                ip_address: activity_tracker.ip(),
+            },
         })
         .await?;
 
diff --git a/crates/handlers/src/oauth2/device/consent.rs b/crates/handlers/src/oauth2/device/consent.rs
index 9f0045ad9..7674e7a4e 100644
--- a/crates/handlers/src/oauth2/device/consent.rs
+++ b/crates/handlers/src/oauth2/device/consent.rs
@@ -87,6 +87,9 @@ pub(crate) async fn get(
             client: &client,
             scope: &grant.scope,
             user: Some(&session.user),
+            requester: mas_policy::Requester {
+                ip_address: activity_tracker.ip(),
+            },
         })
         .await?;
     if !res.valid() {
@@ -167,6 +170,9 @@ pub(crate) async fn post(
             client: &client,
             scope: &grant.scope,
             user: Some(&session.user),
+            requester: mas_policy::Requester {
+                ip_address: activity_tracker.ip(),
+            },
         })
         .await?;
     if !res.valid() {
diff --git a/crates/handlers/src/oauth2/registration.rs b/crates/handlers/src/oauth2/registration.rs
index 1dcba9f65..a32c77caf 100644
--- a/crates/handlers/src/oauth2/registration.rs
+++ b/crates/handlers/src/oauth2/registration.rs
@@ -25,7 +25,7 @@ use thiserror::Error;
 use tracing::info;
 use url::Url;
 
-use crate::impl_from_error_for_route;
+use crate::{impl_from_error_for_route, BoundActivityTracker};
 
 #[derive(Debug, Error)]
 pub(crate) enum RouteError {
@@ -195,6 +195,7 @@ pub(crate) async fn post(
     clock: BoxClock,
     mut repo: BoxRepository,
     mut policy: Policy,
+    activity_tracker: BoundActivityTracker,
     State(encrypter): State<Encrypter>,
     body: Result<Json<ClientMetadata>, axum::extract::rejection::JsonRejection>,
 ) -> Result<impl IntoResponse, RouteError> {
@@ -247,6 +248,9 @@ pub(crate) async fn post(
     let res = policy
         .evaluate_client_registration(mas_policy::ClientRegistrationInput {
             client_metadata: &metadata,
+            requester: mas_policy::Requester {
+                ip_address: activity_tracker.ip(),
+            },
         })
         .await?;
     if !res.valid() {
diff --git a/crates/handlers/src/oauth2/token.rs b/crates/handlers/src/oauth2/token.rs
index 70705293e..e89eb34d7 100644
--- a/crates/handlers/src/oauth2/token.rs
+++ b/crates/handlers/src/oauth2/token.rs
@@ -681,6 +681,9 @@ async fn client_credentials_grant(
             client,
             scope: &scope,
             grant_type: mas_policy::GrantType::ClientCredentials,
+            requester: mas_policy::Requester {
+                ip_address: activity_tracker.ip(),
+            },
         })
         .await?;
     if !res.valid() {
diff --git a/crates/handlers/src/rate_limit.rs b/crates/handlers/src/rate_limit.rs
index eff30d86f..673cee0a6 100644
--- a/crates/handlers/src/rate_limit.rs
+++ b/crates/handlers/src/rate_limit.rs
@@ -53,6 +53,12 @@ pub struct RequesterFingerprint {
     ip: Option<IpAddr>,
 }
 
+impl From<RequesterFingerprint> for mas_policy::Requester {
+    fn from(val: RequesterFingerprint) -> Self {
+        mas_policy::Requester { ip_address: val.ip }
+    }
+}
+
 impl std::fmt::Display for RequesterFingerprint {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         if let Some(ip) = self.ip {
diff --git a/crates/handlers/src/upstream_oauth2/link.rs b/crates/handlers/src/upstream_oauth2/link.rs
index ec22c2c52..cccb3d961 100644
--- a/crates/handlers/src/upstream_oauth2/link.rs
+++ b/crates/handlers/src/upstream_oauth2/link.rs
@@ -43,7 +43,8 @@ use super::{
     UpstreamSessionsCookie,
 };
 use crate::{
-    impl_from_error_for_route, views::shared::OptionalPostAuthAction, PreferredLanguage, SiteConfig,
+    impl_from_error_for_route, views::shared::OptionalPostAuthAction, BoundActivityTracker,
+    PreferredLanguage, SiteConfig,
 };
 
 const DEFAULT_LOCALPART_TEMPLATE: &str = "{{ user.preferred_username }}";
@@ -199,6 +200,7 @@ pub(crate) async fn get(
     State(url_builder): State<UrlBuilder>,
     State(homeserver): State<BoxHomeserverConnection>,
     cookie_jar: CookieJar,
+    activity_tracker: BoundActivityTracker,
     user_agent: Option<TypedHeader<headers::UserAgent>>,
     Path(link_id): Path<Ulid>,
 ) -> Result<impl IntoResponse, RouteError> {
@@ -445,6 +447,9 @@ pub(crate) async fn get(
                                 registration_method: mas_policy::RegistrationMethod::UpstreamOAuth2,
                                 username: &localpart,
                                 email: None,
+                                requester: mas_policy::Requester {
+                                    ip_address: activity_tracker.ip(),
+                                },
                             })
                             .await?;
 
@@ -502,6 +507,7 @@ pub(crate) async fn post(
     user_agent: Option<TypedHeader<headers::UserAgent>>,
     mut policy: Policy,
     PreferredLanguage(locale): PreferredLanguage,
+    activity_tracker: BoundActivityTracker,
     State(templates): State<Templates>,
     State(homeserver): State<BoxHomeserverConnection>,
     State(url_builder): State<UrlBuilder>,
@@ -760,6 +766,9 @@ pub(crate) async fn post(
                     registration_method: mas_policy::RegistrationMethod::UpstreamOAuth2,
                     username: &username,
                     email: email.as_deref(),
+                    requester: mas_policy::Requester {
+                        ip_address: activity_tracker.ip(),
+                    },
                 })
                 .await?;
 
diff --git a/crates/handlers/src/views/register/password.rs b/crates/handlers/src/views/register/password.rs
index 0cc59cbe3..8ce2677ed 100644
--- a/crates/handlers/src/views/register/password.rs
+++ b/crates/handlers/src/views/register/password.rs
@@ -237,6 +237,9 @@ pub(crate) async fn post(
                 registration_method: mas_policy::RegistrationMethod::Password,
                 username: &form.username,
                 email: Some(&form.email),
+                requester: mas_policy::Requester {
+                    ip_address: activity_tracker.ip(),
+                },
             })
             .await?;
 
diff --git a/crates/policy/src/lib.rs b/crates/policy/src/lib.rs
index bd338714f..44da50d38 100644
--- a/crates/policy/src/lib.rs
+++ b/crates/policy/src/lib.rs
@@ -307,6 +307,7 @@ mod tests {
                 registration_method: RegistrationMethod::Password,
                 username: "hello",
                 email: Some("hello@example.com"),
+                requester: Requester { ip_address: None },
             })
             .await
             .unwrap();
@@ -317,6 +318,7 @@ mod tests {
                 registration_method: RegistrationMethod::Password,
                 username: "hello",
                 email: Some("hello@foo.element.io"),
+                requester: Requester { ip_address: None },
             })
             .await
             .unwrap();
@@ -327,6 +329,7 @@ mod tests {
                 registration_method: RegistrationMethod::Password,
                 username: "hello",
                 email: Some("hello@staging.element.io"),
+                requester: Requester { ip_address: None },
             })
             .await
             .unwrap();
diff --git a/crates/policy/src/model.rs b/crates/policy/src/model.rs
index 4e9539e2b..d89b16779 100644
--- a/crates/policy/src/model.rs
+++ b/crates/policy/src/model.rs
@@ -9,6 +9,8 @@
 //! This is useful to generate JSON schemas for each input type, which can then
 //! be type-checked by Open Policy Agent.
 
+use std::net::IpAddr;
+
 use mas_data_model::{Client, User};
 use oauth2_types::{registration::VerifiedClientMetadata, scope::Scope};
 use serde::{Deserialize, Serialize};
@@ -92,6 +94,15 @@ impl EvaluationResult {
     }
 }
 
+/// Identity of the requester
+#[derive(Serialize, Debug, Default)]
+#[serde(rename_all = "snake_case")]
+#[cfg_attr(feature = "jsonschema", derive(schemars::JsonSchema))]
+pub struct Requester {
+    /// IP address of the entity making the request
+    pub ip_address: Option<IpAddr>,
+}
+
 #[derive(Serialize, Debug)]
 #[cfg_attr(feature = "jsonschema", derive(schemars::JsonSchema))]
 pub enum RegistrationMethod {
@@ -113,6 +124,8 @@ pub struct RegisterInput<'a> {
 
     #[serde(skip_serializing_if = "Option::is_none")]
     pub email: Option<&'a str>,
+
+    pub requester: Requester,
 }
 
 /// Input for the client registration policy.
@@ -125,6 +138,7 @@ pub struct ClientRegistrationInput<'a> {
         schemars(with = "std::collections::HashMap<String, serde_json::Value>")
     )]
     pub client_metadata: &'a VerifiedClientMetadata,
+    pub requester: Requester,
 }
 
 #[derive(Serialize, Debug)]
@@ -158,6 +172,8 @@ pub struct AuthorizationGrantInput<'a> {
     pub scope: &'a Scope,
 
     pub grant_type: GrantType,
+
+    pub requester: Requester,
 }
 
 /// Input for the email add policy.
@@ -167,4 +183,5 @@ pub struct AuthorizationGrantInput<'a> {
 pub struct EmailInput<'a> {
     pub email: &'a str,
 
+    pub requester: Requester,
 }
diff --git a/policies/register/register.rego b/policies/register/register.rego
index 0fb36bf37..c3836d170 100644
--- a/policies/register/register.rego
+++ b/policies/register/register.rego
@@ -13,6 +13,26 @@ allow if {
 	count(violation) == 0
 }
 
+# Normalize an IP address or CIDR to a CIDR
+normalize_cidr(ip) := ip if contains(ip, "/")
+
+# If it's an IPv4, append /32
+normalize_cidr(ip) := sprintf("%s/32", [ip]) if {
+	not contains(ip, "/")
+	not contains(ip, ":")
+}
+
+# If it's an IPv6, append /128
+normalize_cidr(ip) := sprintf("%s/128", [ip]) if {
+	not contains(ip, "/")
+	contains(ip, ":")
+}
+
+is_ip_banned(ip) if {
+	some cidr in data.registration.banned_ips
+	net.cidr_contains(normalize_cidr(cidr), ip)
+}
+
 mxid(username, server_name) := sprintf("@%s:%s", [username, server_name])
 
 # METADATA
@@ -48,6 +68,10 @@ violation contains {"msg": "unknown registration method"} if {
 	not input.registration_method in ["password", "upstream-oauth2"]
 }
 
+violation contains {"msg": "IP address is banned"} if {
+	is_ip_banned(input.requester.ip_address)
+}
+
 # Check that we supplied an email for password registration
 violation contains {"field": "email", "msg": "email required for password-based registration"} if {
 	input.registration_method == "password"
diff --git a/policies/register/register_test.rego b/policies/register/register_test.rego
index 26e119248..cf4324fa2 100644
--- a/policies/register/register_test.rego
+++ b/policies/register/register_test.rego
@@ -74,3 +74,19 @@ test_invalid_username if {
 test_numeric_username if {
 	not register.allow with input as {"username": "1234", "registration_method": "upstream-oauth2"}
 }
+
+test_ip_ban if {
+	not register.allow with input as {
+		"username": "hello",
+		"registration_method": "upstream-oauth2",
+		"requester": {"ip_address": "1.1.1.1"},
+	}
+		with data.registration.banned_ips as ["1.1.1.1"]
+
+	not register.allow with input as {
+		"username": "hello",
+		"registration_method": "upstream-oauth2",
+		"requester": {"ip_address": "1.1.1.1"},
+	}
+		with data.registration.banned_ips as ["1.0.0.0/8"]
+}
diff --git a/policies/schema/authorization_grant_input.json b/policies/schema/authorization_grant_input.json
index 9b2f77403..5c431b431 100644
--- a/policies/schema/authorization_grant_input.json
+++ b/policies/schema/authorization_grant_input.json
@@ -6,6 +6,7 @@
   "required": [
     "client",
     "grant_type",
+    "requester",
     "scope"
   ],
   "properties": {
@@ -22,6 +23,9 @@
     },
     "grant_type": {
       "$ref": "#/definitions/GrantType"
+    },
+    "requester": {
+      "$ref": "#/definitions/Requester"
     }
   },
   "definitions": {
@@ -32,6 +36,17 @@
         "client_credentials",
         "urn:ietf:params:oauth:grant-type:device_code"
       ]
+    },
+    "Requester": {
+      "description": "Identity of the requester",
+      "type": "object",
+      "properties": {
+        "ip_address": {
+          "description": "IP address of the entity making the request",
+          "type": "string",
+          "format": "ip"
+        }
+      }
     }
   }
 }
\ No newline at end of file
diff --git a/policies/schema/client_registration_input.json b/policies/schema/client_registration_input.json
index cc9957a85..096c56a0a 100644
--- a/policies/schema/client_registration_input.json
+++ b/policies/schema/client_registration_input.json
@@ -4,12 +4,29 @@
   "description": "Input for the client registration policy.",
   "type": "object",
   "required": [
-    "client_metadata"
+    "client_metadata",
+    "requester"
   ],
   "properties": {
     "client_metadata": {
       "type": "object",
       "additionalProperties": true
+    },
+    "requester": {
+      "$ref": "#/definitions/Requester"
+    }
+  },
+  "definitions": {
+    "Requester": {
+      "description": "Identity of the requester",
+      "type": "object",
+      "properties": {
+        "ip_address": {
+          "description": "IP address of the entity making the request",
+          "type": "string",
+          "format": "ip"
+        }
+      }
     }
   }
 }
\ No newline at end of file
diff --git a/policies/schema/email_input.json b/policies/schema/email_input.json
index 19f4af523..384c359b6 100644
--- a/policies/schema/email_input.json
+++ b/policies/schema/email_input.json
@@ -4,11 +4,28 @@
   "description": "Input for the email add policy.",
   "type": "object",
   "required": [
-    "email"
+    "email",
+    "requester"
   ],
   "properties": {
     "email": {
       "type": "string"
+    },
+    "requester": {
+      "$ref": "#/definitions/Requester"
+    }
+  },
+  "definitions": {
+    "Requester": {
+      "description": "Identity of the requester",
+      "type": "object",
+      "properties": {
+        "ip_address": {
+          "description": "IP address of the entity making the request",
+          "type": "string",
+          "format": "ip"
+        }
+      }
     }
   }
 }
\ No newline at end of file
diff --git a/policies/schema/register_input.json b/policies/schema/register_input.json
index e1d796ea1..27a19b78c 100644
--- a/policies/schema/register_input.json
+++ b/policies/schema/register_input.json
@@ -2,49 +2,44 @@
   "$schema": "http://json-schema.org/draft-07/schema#",
   "title": "RegisterInput",
   "description": "Input for the user registration policy.",
-  "oneOf": [
-    {
-      "type": "object",
-      "required": [
-        "email",
-        "registration_method",
-        "username"
-      ],
-      "properties": {
-        "registration_method": {
-          "type": "string",
-          "enum": [
-            "password"
-          ]
-        },
-        "username": {
-          "type": "string"
-        },
-        "email": {
-          "type": "string"
-        }
-      }
+  "type": "object",
+  "required": [
+    "registration_method",
+    "requester",
+    "username"
+  ],
+  "properties": {
+    "registration_method": {
+      "$ref": "#/definitions/RegistrationMethod"
     },
-    {
+    "username": {
+      "type": "string"
+    },
+    "email": {
+      "type": "string"
+    },
+    "requester": {
+      "$ref": "#/definitions/Requester"
+    }
+  },
+  "definitions": {
+    "RegistrationMethod": {
+      "type": "string",
+      "enum": [
+        "password",
+        "upstream-oauth2"
+      ]
+    },
+    "Requester": {
+      "description": "Identity of the requester",
       "type": "object",
-      "required": [
-        "registration_method",
-        "username"
-      ],
       "properties": {
-        "registration_method": {
+        "ip_address": {
+          "description": "IP address of the entity making the request",
           "type": "string",
-          "enum": [
-            "upstream-oauth2"
-          ]
-        },
-        "username": {
-          "type": "string"
-        },
-        "email": {
-          "type": "string"
+          "format": "ip"
         }
       }
     }
-  ]
+  }
 }
\ No newline at end of file