diff --git a/src/smtp/smtp.ts b/src/smtp/smtp.ts
index 1d87c53..773e90d 100644
--- a/src/smtp/smtp.ts
+++ b/src/smtp/smtp.ts
@@ -28,7 +28,7 @@ export const checkSMTP = async (
         socket.emit('fail', 'Mail server closed connection without sending any data.')
       }
     })
-    socket.on('fail', msg => {
+    socket.once('fail', msg => {
       r(createOutput('smtp', msg))
       if (socket.writable && !socket.destroyed) {
         socket.write(`quit\r\n`)