不幸的是，我发给客户的邮件立即被退回了。

Unfortunately, the email I sent to the client ___bounce ___back immediately.

如果你在地址中输错了域名，邮件常常会被退回。

Messages often ___bounce ___back if you mistype the domain name in the address.

由于服务器故障，我的紧急提案被退回，造成了严重的延误。

My urgent proposal ___bounce ___back due to a server outage, causing significant delays.