diff --git a/src/sendSlackMessage.js b/src/sendSlackMessage.js
index e068d94f..cecee4bc 100644
--- a/src/sendSlackMessage.js
+++ b/src/sendSlackMessage.js
@@ -1,3 +1,22 @@
+async function findChannelId (web, name) {
+  let cursor = null
+
+  while (true) {
+    const r = await web.conversations.list({ cursor })
+    const f = r.channels.find(c => c.name === name || c.name === name.substring(1))
+
+    if (f) {
+      return f.id
+    }
+
+    if (!r.response_metadata.next_cursor) {
+      throw new Error('channel not found')
+    }
+
+    cursor = r.response_metadata.next_cursor
+  }
+}
+
 // send markdown message to slack channel
 export default async function sendSlackMessage ({
   token = null,
@@ -22,14 +41,21 @@ export default async function sendSlackMessage ({
 
   if (debug) { console.log(`token.length: ${token.length}, channel: ${channel}, message: ${message}`) }
 
-  const { WebClient } = await import('@slack/web-api')
   const { markdownToBlocks } = await import('@tryfabric/mack')
+  const { WebClient } = await import('@slack/web-api')
 
   const web = new WebClient(token)
   let blocks = await markdownToBlocks(message)
 
+  // calculate the sha256 hash of the message
+  const crypto = await import('crypto')
+  const hash = crypto.createHash('sha256')
+  hash.update(message)
+  const hashHex = hash.digest('hex')
+
   if (debug) { console.log(blocks) }
 
+  // slack blocks have a limit of 50 blocks, remove the last blocks if there are more
   if (blocks.length > 50) {
     blocks = blocks.slice(0, 49)
     blocks.push({
@@ -41,11 +67,30 @@ export default async function sendSlackMessage ({
     })
   }
 
+  // get the channel id
+  const channelId = await findChannelId(web, channel)
+
+  // get last 50 messages from the channel, in the last day
+  const history = await web.conversations.history({
+    channel: channelId,
+    limit: 50,
+    oldest: Date.now() / 1000 - 60 * 60 * 24 // a day ago
+  })
+
+  // debounce messages if the same message was sent in the last day
+  if (history.messages.some(m => m.metadata?.event_type === hashHex)) {
+    throw new Error('debounce message')
+  }
+
+  const metadata = { event_type: hashHex, event_payload: { } }
+
+  // send the message
   const result = await web.chat.postMessage({
     username,
     text: `${username} alert`,
     channel,
-    blocks
+    blocks,
+    metadata
   })
 
   if (debug) { console.log(`result: ${JSON.stringify(result)}`) }