我已经从我的 GMail 帐户发送了一封邮件，一天后收到了以下回复。
This is an automatically generated Delivery Status Notification
THIS IS A WARNING MESSAGE ONLY.
YOU DO NOT NEED TO RESEND YOUR MESSAGE.
Delivery to the following recipient has been delayed:
Message will be retried for 2 more day(s)
Technical details of temporary failure:
The recipient server did not accept our requests to connect
谁能解释我为什么收到这个？