Improve error handling in send method by logging response on failure

micromail.py

@@ -189,9 +189,10 @@ class MicromailClient:
         self.write(content + b"\r\n")
 
     def send(self):
-        code, _ = self.send_command(b"\r\n.")
+        code, res = self.send_command(b"\r\n.")
         if code != b"250":
             print(f"Error: got code {code} on send")
+            print(res)
             sys.exit(1)
         print("Message sent successfully")