我的邮件被退回了，因为我输错了地址。

My email ___bounced because I mistyped the address.

由于服务器问题，昨天所有外发邮件都被退回了。

Due to a server issue, all outgoing messages ___bounced yesterday.

有几封重要的通知邮件被退回到了我们的系统。

Several important notifications have ___bounced back to our system.