The unofficial U.S. postal creed says neither rain, nor sleet, nor heat, nor gloom of night will keep carriers from their rounds.
Thieves and vicious dogs, however, may be another matter.
So the Post Office is delivering a solution.
In broad daylight in Washington, D.C. last year, two armed men attacked a U.S. letter carrier. He was beaten, bound and robbed.
It was one of more than 400 assaults on postal workers nationwide in 2014, up nine percent in the past five years.
That same year, dogs attacked carriers more than 5,700 times.
Virginia carrier Nilo Parin was one of them. The Postal Service had given Parin no way to call for help until now.
The Postal Service is shipping all 230,000 carriers new mobile devices with a soon-to-be-activated "panic button."
GPS transmits their location to their supervisors every minute.
Jeff Williamson is the chief of human resources for the Postal Service and gave the first public look at the devices, which will be rolled out by September.
The new devices also let supervisors warn carriers with alerts like they did during the recent unrest in Baltimore.
"So when you think about the power of this, the safety element of what this allows us to do from a carrier-standpoint is just incredible," Williamson said.
The devices also allow virtually real-time notifications when packages have arrived and more efficient routes to save time and fuel.
The Postal Service is spending $200 million on this. That's a lot of money, especially for an organization that lost $5 billion last year and wants to cut Saturday delivery.
"It's an investment in our future is what it is," said Dave Williams, the Postal Service COO. "It's an investment in the growth of our organization."
And for those who carry that mail, the new devices are delivering a sense of security.
Does it make Parin feel safer? "It does," he said.