diff --git a/backend/api/package.json b/backend/api/package.json
index cd4331b8..81e4af39 100644
--- a/backend/api/package.json
+++ b/backend/api/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@compass/api",
-  "version": "1.42.1",
+  "version": "1.43.0",
   "private": true,
   "description": "Backend API endpoints",
   "main": "src/serve.ts",
diff --git a/backend/api/src/create-comment.ts b/backend/api/src/create-comment.ts
index 26a5f401..d3c7bf6e 100644
--- a/backend/api/src/create-comment.ts
+++ b/backend/api/src/create-comment.ts
@@ -1,5 +1,6 @@
 import {type JSONContent} from '@tiptap/core'
 import {APIErrors, APIHandler} from 'api/helpers/endpoint'
+import {isSuspiciousId} from 'common/moderation/suspicious'
 import {Notification} from 'common/notifications'
 import {convertComment} from 'common/supabase/comment'
 import {type Row} from 'common/supabase/utils'
@@ -56,6 +57,7 @@ const validateComment = async (userId: string, creatorId: string, content: JSONC
 
   if (!creator) throw APIErrors.unauthorized('Your account was not found')
   if (creator.isBannedFromPosting) throw APIErrors.forbidden('You are banned')
+  if (isSuspiciousId(creator.id)) throw APIErrors.forbidden('Suspicious users cannot send messages')
 
   const otherUser = await getPrivateUser(userId)
   if (!otherUser) throw APIErrors.notFound('Other user not found')
diff --git a/backend/api/src/create-private-user-message.ts b/backend/api/src/create-private-user-message.ts
index eecc6cb1..e72ff9bf 100644
--- a/backend/api/src/create-private-user-message.ts
+++ b/backend/api/src/create-private-user-message.ts
@@ -1,6 +1,7 @@
 import {MAX_COMMENT_JSON_LENGTH} from 'api/create-comment'
 import {APIErrors, APIHandler} from 'api/helpers/endpoint'
 import {createPrivateUserMessageMain} from 'api/helpers/private-messages'
+import {isSuspiciousId} from 'common/moderation/suspicious'
 import {createSupabaseDirectClient} from 'shared/supabase/init'
 import {getUser} from 'shared/utils'
 
@@ -16,6 +17,7 @@ export const createPrivateUserMessage: APIHandler<'create-private-user-message'>
   const creator = await getUser(auth.uid)
   if (!creator) throw APIErrors.unauthorized('Your account was not found')
   if (creator.isBannedFromPosting) throw APIErrors.forbidden('You are banned')
+  if (isSuspiciousId(creator.id)) throw APIErrors.forbidden('Suspicious users cannot send messages')
 
   const pg = createSupabaseDirectClient()
   return await createPrivateUserMessageMain(creator, channelId, content, pg, 'private')
diff --git a/common/src/moderation/suspicious.ts b/common/src/moderation/suspicious.ts
new file mode 100644
index 00000000..a7f8c0b6
--- /dev/null
+++ b/common/src/moderation/suspicious.ts
@@ -0,0 +1,11 @@
+// If used long-term, consider moving to a database (new user column or new table)
+export const suspiciousIds = ['K5Y1nuQopYhvNpnycvKyoNQ1FaK2']
+
+// Suspicious users are flagged in between legit and banned:
+// They still have access to the app (including viewing profiles), but are not allowed to
+// interact too heavily with people so as not to bother them (no DMs or endorsements)
+// Mark a user as suspicious if they message too many people or if they get reported once
+// (ban them if reported more than once)
+export function isSuspiciousId(id: string) {
+  return suspiciousIds.includes(id)
+}