diff --git a/src/transport/smtp/pool/sync_impl.rs b/src/transport/smtp/pool/sync_impl.rs
index 1d78a98..a69ad10 100644
--- a/src/transport/smtp/pool/sync_impl.rs
+++ b/src/transport/smtp/pool/sync_impl.rs
@@ -109,6 +109,7 @@ impl Pool {
                             }
                         }
 
+                        drop(pool);
                         thread::sleep(idle_timeout);
                     }
                 })