diff --git a/src/behaviors/voice.js b/src/behaviors/voice.js
index 0b12dff..1a1dfc3 100644
--- a/src/behaviors/voice.js
+++ b/src/behaviors/voice.js
@@ -1,10 +1,14 @@
 const MemoryBehavior = require('../models/memory-behavior');
 
+// Keep track of which users have already been greeted
+const greetedUsers = new Set();
+
 module.exports = (client) => {
   // should run only on unrecognized users
   const voiceAction = (botNick, username) => {
     var matrix = false;
     if (username.match(/\[m\]/) !== null) matrix = true; // exempt matrix user
+
     if (matrix) {
       //client.client.send('PRIVMSG', 'ChanServ', "");
       client.client.send('MODE', '#publiclab', '+v', username);
@@ -14,7 +18,14 @@ module.exports = (client) => {
       client.client.send('MODE', '#publiclab', '+q', username + '!*@*');
       client.client.send('PRIVMSG', username, 'Welcome; because we have had some spam attacks, folks joining via IRC need to type "/msg plotsbot approve me" approved to chat. We are really sorry for the inconvenience but the spam got really awful!');
       client.client.send('PRIVMSG', username, 'You may not be able to hear messages from other platforms; until this is fixed, see https://publiclab.org/chat to use a different chat system; apologies!');
-      return username + ' just joined via IRC; welcome! They may not hear messages via Riot/Matrix/Gitter/Slack (we are working on this problem), so use https://chat.publiclab.org to respond.';
+
+      // Only greet new users once, when they send their first message
+      if (!greetedUsers.has(username)) {
+        greetedUsers.add(username);
+        return username + ' just joined via IRC; welcome! They may not hear messages via Riot/Matrix/Gitter/Slack (we are working on this problem), so use https://chat.publiclab.org to respond.';
+      } else {
+        return null; // do nothing if already greeted
+      }
     }
   };