diff --git a/client/basic/connection.ts b/client/basic/connection.ts
index 12306f6..467a509 100644
--- a/client/basic/connection.ts
+++ b/client/basic/connection.ts
@@ -22,6 +22,7 @@ export class SMTPConnection {
   ready: Promise<void>;
 
   async close() {
+    await this.ready;
     if (!this.conn) {
       return;
     }