diff --git a/docs/configuration.md b/docs/configuration.md
index eb6edde..ad29ce8 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -222,6 +222,15 @@ Make sure to do the necessary [port forwarding](https://portforward.com/) and ad
 **Default:** `!`  
 Prefix for bot commands
 
+#### reactOnSeen
+**Default:** `off`  
+If enabled, the bot will react to messages sent to it with the emoji defined in `reactOnSeenEmoji`
+
+#### reactOnSeenEmoji
+**Default:** `📨`  
+The emoji that the bot will react with when it sees a message.  Requires `reactOnSeen` to be enabled.  
+Must be pasted in the config file as the Emoji representation and not as a unicode codepoint.
+
 #### relaySmallAttachmentsAsAttachments
 **Default:** `off`  
 If enabled, small attachments from users are sent as real attachments rather than links in modmail threads.
diff --git a/src/data/Thread.js b/src/data/Thread.js
index 2912b11..ffedd55 100644
--- a/src/data/Thread.js
+++ b/src/data/Thread.js
@@ -323,6 +323,10 @@ class Thread {
       await this._updateThreadMessage(threadMessage.id, { inbox_message_id: inboxMessage.id });
     }
 
+    if (config.reactOnSeen) {
+      await msg.addReaction(config.reactOnSeenEmoji);
+    }
+
     // Interrupt scheduled closing, if in progress
     if (this.scheduled_close_at) {
       await this.cancelScheduledClose();
diff --git a/src/data/cfg.schema.json b/src/data/cfg.schema.json
index 198c87a..94738a3 100644
--- a/src/data/cfg.schema.json
+++ b/src/data/cfg.schema.json
@@ -244,6 +244,16 @@
       }
     },
 
+    "reactOnSeen": {
+      "$ref": "#/definitions/customBoolean",
+      "default": false
+    },
+
+    "reactOnSeenEmoji": {
+      "type": "string",
+      "default": "\uD83D\uDCE8"
+    },
+
     "port": {
       "type": "number",
       "maximum": 65535,