diff --git a/post.sh b/post.sh
index f118acb..bf2afdb 100755
--- a/post.sh
+++ b/post.sh
@@ -14,21 +14,46 @@ function exit_error {
     exit "${2-1}"
 }
 
+# Select an entry from the list
+function select_entry {
+    # Select a random entry from the list
+    local entry=$(sort -R finds_you.txt | head -1)
+    # Remove any trailing carriage return from the entry
+    echo "$entry" | tr -d '\r'
+}
+
+# See if an entry has been used in the past 500 posts
+function is_recent {
+    local entry_hash=$(echo -n "$1" | md5sum | cut -d ' ' -f 1)
+    if tail -n 50 post_history.txt | grep -q "$entry_hash"; then
+        return 0  # 0 = true, recent
+    else
+        return 1  # 1 = false, not recent
+    fi
+}
+
 # Move into the directory where this script is found
 cd "$(dirname "$0")" || exit
 
-# Select a random entry from the list
-ENTRY=$(sort -R finds_you.txt |head -1)
-
-# Remove any trailing carriage return from the entry
-ENTRY=$(echo "$ENTRY" | tr -d '\r')
+# Loop until a non-recent entry is found
+while true; do
+    ENTRY=$(select_entry)
+    if is_recent "$ENTRY"; then
+        echo "Entry is recent, selecting another..."
+        continue
+    else
+        break
+    fi
+done
 
 POST="I hope this email ${ENTRY}"
 
 # Send the message to Mastodon
 curl "$MASTODON_SERVER"/api/v1/statuses -H "Authorization: Bearer ${MASTODON_TOKEN}" -F "status=${POST}"
-
 RESULT=$?
 if [ "$RESULT" -ne 0 ]; then
     exit_error "Posting message to Mastodon failed"
 fi
+
+# Log this to the post history
+echo -n "$ENTRY" | md5sum | cut -d ' ' -f 1 >> post_history.txt