OOO       
noun [ C ] uk/ˌəʊ.əʊˈəʊ/ us/ˌoʊ.oʊˈoʊ/
 不在办公室(out of office 的缩写)
abbreviation for out of office: a reply that can be automatically sent to an email that you have received when you are not in the office and cannot reply personally, or the system for sending such a reply
  For fun OOO messages, they have created an Out of Office generator.  他们开发了一款“不在办公室”生成器,可以发出各种好玩的OOO信息。 
 I've put my OOO on. 我已经打开了”不在办公室“的自动回复。 
 - More examples
 - Remember that if a perfect stranger emails you, they will also receive your OOO.
 - Many people said that setting their OOO feels as if vacation is officially starting.
 - 66% of respondents said they like seeing creative OOOs from other people.