Post office officials say Green Bay's processing and distribution center usually handles about 300,000 letters per day.
However, with many sending out seasonal holiday cards, the plant is seeing a surge in numbers.
"In our delivery unit we get about three times the letters every day that we delivery and Monday, I think we had probably four times the number of packages," Green Bay postmaster Jane Wittkopf says.
This coming Monday, December 16th, is expected to be its busiest mailing day this year.
More than one million letters will be processed.