postal       
adjective uk/ˈpəʊ.stəl/ us/ˈpoʊ.stəl/
C1 邮件的;邮政的
relating to post or to the public service that collects and delivers the post
  postal charges 邮资 
 the postal service 邮政服务 
 a postal strike 邮政罢工 
 postal workers 邮政工人 
 - More examples
 - None of my birthday cards arrived because of a postal strike.
 - The new chairman was elected by a postal ballot.
 - UK You can pay by cheque or postal order.
 - Postal workers are currently on strike.
 - Elderly or disabled people may be eligible for a postal vote.
 
Idiom   
go postalidiom US informal 非常愤怒而做出狂暴行为的
to become very angry and do something violent
  The man went postal and shot twelve of his colleagues. 这个男人变得很疯狂,枪击了他的十二个同事。