This is a circa 1900 stoneware foot warmer and definitely not a maple syrup container. It was produced in England where the mailboxes have a distinctly different form and shape from those in America. Yours was produced by Lovatt and Lovatt and their Langley Mill Pottery. These pieces were filled with boiling hot water and placed under the sheets at the foot of the bed as a warmer in the cold weather seasons.
The estimate is based on actual recent past recorded auction sales of comparables. Retail 'asking prices' can be higher and vary.