Definitions
American Heritage® Dictionary of the English Language, Fourth Edition
- adj. Of or relating to a post office or mail service.
- idiom. go postal Slang To become extremely angry or deranged, especially in an outburst of violence.
Century Dictionary and Cyclopedia
- Relating to the post or mails; belonging or pertaining to a mail service: as, postal arrangements; postal regulations; postal service.
- Called post-cards in the United Kingdom.
- n. A postal card or postal order.
Wiktionary
- adj. Relating to the collection, sorting and delivery of mail.
GNU Webster's 1913
- adj. Belonging to the post office or mail service
WordNet 3.0
- adj. of or relating to the system for delivering mail
Examples
“Many in postal management are driven only by securing higher pay and bonuses.”
“Strong mail volume this month might add enough revenue to justify making the $5.5 billion payment to the government, but it would still leave little in postal coffers, said sources familiar with the process but not authorized to speak on the record.”
“But he's looking to reduce the mail agency's real estate portfolio by focusing more on expanding about 100,000 "access points" where people can obtain postal goods and services -- locations ranging from Office Depots to pharmacies with stamp machines.”
The Washington Post: The Federal Eye: Meet the new postmaster general
“With the increase in postal rates no one is happy.”
John Donahoe’s Plan to Save eBay: Better Search - Bits Blog - NYTimes.com
“Well that is due to the huge rise in postal voting.”
“As a result expect to see an increase in postal voting especially in marginal seats.”
“Ministers were warned as long ago as May 2000 about the lack of security in postal votes.”
“The Time Warner plan offered various incentives that could only be realized by large publishing groups, such as co-palletizing large numbers of magazines together or drop shipping from within postal zones via centralized printing and distribution centers.”
“Beginning next April, a staggering $1 trillion in long-term postal deposits will mature, creating a potential shift from savings accounts to stock markets unprecedented in Japanese history.”
“I read exactly zero of these: S But its not that I haven't been trying, and going postal is now on my list”
Lists
‘postal’ hasn't been added to any lists yet.

bilby Thanks yarb, that makes sense. I had been wondering what mild-mannered posties might have done to become the epitome of fury/exuberance. Jan 9, 2011
yarb I believe it's that (U.S.) post offices were famous for driving their employees and customers to rage / insanity. I'm surprised you'd not heard it before - although I'm not sure I've heard it in that sense of pure excitement.
Good spot! Jan 9, 2011
bilby I'd never heard 'go postal' until this, yesterday:
"Stevenage goal: Would you Adam it? Michael Bostwick stings a beauty in off the far post from range to double Stevenage's lead... and Broadhall Way goes absolutely postal."
- Sam Lyon, FA Cup as it happened, BBC website, 8 Jan 2011.
In this context there was no connotation of violence, simply of wild celebration.
Does anybody know the origin of the expression? Jan 9, 2011
skipvia In the vernacular, to lose control and commit an irrational, usually violent act. Dec 20, 2007