Narcotics were sent from various packaging centres, some with fake stamps.
Since last winter, the police have stopped 17,000 packages – and identified thousands of buyers.
The new postal law that came into effect last year means that Postnord and other postal operators can now tip off the police about suspicious letters and packages.
Since last winter, 17,000 packages containing, among other things, narcotics and doping substances have been seized.
"The handling of illegal postal items is highly organised. It's about proper packaging centres where people are paid to handle them," says Johan Ekström, investigation leader in police region West, in a press release.
"In some cases, the packages were sent to Sweden solely for the purpose of packing and posting the items for payment."
About 30 people are currently in custody, suspected of serious and aggravated narcotics offences. The first charges are likely to be brought this summer.
Meanwhile, the investigation into thousands of suspected buyers is ongoing. According to Ekot on Sveriges Radio, it's over 10,000 people who have or are expected to be contacted by the police.
"Many suspects are previously unconvicted and usually have an orderly life with a job and family. If there are minors involved, the police make a report to social services," says Johan Ekström.
