Finchingfield Post Office will close for eight days for a refurbishment.
The Bardfield Road branch will shut on September 2 at 5.30pm and re-open on September 10.
Its opening hours will be extended to Monday to Friday 7.30am to 5.30pm and Saturday and Sunday 9am to 1pm.
This is an extra 11 hours 30 minutes a week, including Sunday and earlier opening.
The size of the retail area, which specialises in fresh local produce, will also nearly double.