Criminals who posted drugs to customers in the mail were caught after postal staff became suspicious and called police.
Royal Mail intercepted around 1,800 parcels that had been posted in and around Chelmsford in November and December 2018.
The drugs had an estimated street value of up to £517,500 and included crack cocaine, heroin, MDMA, cannabis, ketamine, LSD, crystal meth, amphetamine and ecstasy.
They were due to be sent to addresses across the UK, as well as Australia and America.
Suspicions were first raised when 54 parcels arrived in the sorting office over the course of four days, all of them smelling strongly of cannabis.
Police were called and detectives began an investigation to identify who was sending them.
On December 19, 2018, officers arrested Charles Willoughby a few minutes after he was seen posting envelopes into a post box in London Road, Brentwood. The packages were retrieved and found to contain cannabis bud.
On the same day, officers executed a search warrant at a flat he rented in Rollason Way, Brentwood. His brother James Willoughby was seen jumping from a balcony and trying to escape, but was arrested.
Inside the house were large boxes of padded envelopes identical to those already seized by police and cannabis bud.
Officers also searched a flat in Watson Heights, Chelmsford, an address linked to Mac Cheremeh and James Willoughby, where they found more cannabis bud and £1,000 cash.
They also searched a house linked to James Willoughby in Broomfield Road, Chelmsford, where they found packaging items and the drugs.
Following an extensive investigation, the three men were summonsed to court in December 2019.
James Willoughby, 27, of Islay Walk, Islington, and Cheremeh, 42, of Lingwood Road, Hackney, each admitted three charges of conspiracy to supply class A drugs and two charges of conspiracy to supply class B drugs when they appeared at Chelmsford Crown Court on January 21 this year.
Charles Willoughby, 32, of Rollason Way, Brentwood, admitted conspiracy to supply a class B drug.
They returned to court on Wednesday August 19 where James Willoughby and Cheremeh were each jailed for ten years.
Charles Willoughby was given an eight-month jail term, suspended for two years.
The drugs, paraphernalia, mobile phones and computer and technical equipment used in their operation were seized and will be destroyed.
A Proceeds of Crime hearing will be held in due course.