New Zealand Post was on track to process up to seven million parcels this month, up from 6.5 million last December.
Mr Gallagher said shopping mall customers already stressed about car parking, big crowds, and other frustrations sometimes vented their anger at PostShop workers.
"It's a bit like road rage. They get inside the building and they have building rage."
Mr Gallagher said this time of year was "manic" for most PostShops and it would probably stay busy until the second week of January.
He said many people buy gifts at Boxing Day shopping sprees for posting.
Mr Gallagher said this festive season's statistics showed post remained "a critical piece of infrastructure".
He said although fewer people sent letters, it was a different story for parcels.Online shopping at local and overseas websites was boosting demand.
"People are buying a lot of stuff offshore. The product mix is changing."
Mr Gallagher said the boom in parcels and packages was great news for postal workers.