Here is a good idea. Keep your mandevilla containerized, but let it accent your mailbox until frost.
Mandevilla flowers are a bright and colorful addition but will not over winter outside.
Mandevilla is a popular tropical vine that is treated as an annual vine here in the Metro area. Since they will not overwinter outdoors here, most of the time they are grown in containers. As the weather cools a bit, it seems to take on a rebirth and starts flowering profusely. The tropical vine must be trained on a structure and likes full sun, but will do okay in part shade with a reduced amount of blooms. Many folks overwinter theirs, if they get it indoors before the night temperature fall below freezing. But I generally compost them after a freeze and buy a new the next spring. The one you see here is Alice du Pont, and it is the most popular one. They like water and fertilization to do their best. There are other colors and a dwarf selection, but Alice du Pont is still my favorite.