The thefts were discovered after a hidden surveillance camera was installed over her work area following a tip, the Sydsvenskan newspaper reported.
The woman, who worked in mail sorting, would open colourful greeting envelopes, then pocket their contents.
Posten began its investigation in mid-September 2010, using the filmed material as evidence and the woman was arrested at the end of the month.
Upon being reported to the police, the woman confessed immediately. A subsequent search of her home uncovered large quantities of gift certificates, discount vouchers and lottery tickets, Sydsvenskan reported.
A Posten investigator told police estimated the woman could have stolen anywhere from a few hundred to several thousand kronor per day.
Several birthday cards, invitations and thank you cards were also found and police have managed to trace the majority of those concerned. A number of companies who sent gift cards have also been contacted in connection with the investigation.
The woman has been charged with breaching postal confidentiality and theft.