It is hoped 20,000 stolen mail items will be in the hands of the intended recipients by Christmas, following the arrest of a Queenstown postie on November 9.
Detective Sergeant Brian Cameron said each piece of unopened mail had to be compiled and catalogued, though the process was near completion.
It is estimated 2% to 3% of the mail was opened by the 32-year-old woman and Det Sgt Cameron said this involved "a bit more investigation".
Speaking yesterday, he said on Monday there were four officers, including a detective, looking at the opened mail and police are trying to determine what the woman may have taken.
The woman has interim name suppression and has been charged with theft by a person in a special relationship.
Det Sgt Cameron would not comment on whether more charges might be laid.
Once police had finished cataloguing mail, it would be handed back to New Zealand Post who would determine the delivery schedule.
Det Sgt Cameron said there was no intention by either NZ Post or the police to delay delivery, but as a crime had been committed, police were obliged to record all evidence.
"Unopened mail will certainly be released for NZ Post to deliver shortly."
When asked whether the mail would be returned before Christmas, he said he "would imagine so" but would not make any promises due to the scale of the crime and because the mail would soon be transferred from police hands to NZ Post.
Mail was first found at the woman's house in Frankton, which she shared with flatmates, and less than a week later on November 15 police executed a search warrant at an Arrowtown storage unit which resulted in the discovery of more mail.
The stolen mail belongs to Fernhill, Lakes Hayes Estate and Arrowtown residents.
NZ Post media communications manager Michael Tull earlier told the Otago Daily Times the company would investigate its delivery processes and try to identify whether the incident could have been avoided.