Jabur Hissan buried more than 29,000 letters in his garden and on wasteland, burned 400 more and dumped nearly 200 on a canal towpath.
Some of the post should have been delivered to houses the father-of-two walked past on his way back to his home in Birmingham.
The 32-year-old was told he had created a “devastating security risk” and was jailed for eight months.
“There is a serious risk, there were bills in the mail and people were not able to meet their responsibilities, letters to loved ones and more,” District Judge Jack McGarthar said.
“This has a devastating effect on anybody affected by it.
“Postmen are in a position of very high trust and you have seriously breached that position.”
Hissan admitted charges of arson, criminal damage to property worth more than £5,000 and delaying post.
The offences covered a total of 29,178 items.
John Dove, prosecuting, told Birmingham Magistrates’ Court that some of the dumped letters had turned to ‘pulp’.
He said: “Most of the items were in very poor condition as they had been exposed to the elements and left rotting.
“Some of the packets had been dumped in vegetation and trampled into the ground, suggesting an attempt had been made to bury them, and some were mere pulp.”
Robert Skinner, defending, said Hissan believed he was ditching junk mail.
Mr Skinner said: “He was at the bottom of the rung and, I suspect, on the bottom pay package offered by the Royal Mail.
“He was finding it difficult to keep up with his rounds and he was struggling at home to bring up a young family, one of whom was requiring regular medical treatment for eczema.
“It was of his view that it was junk mail that he was not delivering.”
But the judge said to Hissan: “The items described as junk mail by your solicitor are certainly not junk to the people who pay for them to be delivered.
“The Royal Mail depend entirely in postmen to act faithfully and deliver items placed into their trust.”