Abstract: Disclosed is a mailbox slider device that provides mailboxes of various widths to be slideably mounted along the horizontal portion of an existing mailbox support post. The device comprises a first base member and a second slideable member being attached using complimentary tongue and groove sliders, wherein the members include a recessed channel having a first and second channel stop that prevents separation of the two members at the base member distal end, while allowing separation and engagement of the members along the inward proximal end of the base member. A mailbox is secured to a support block, which then attaches to the upper surface of the second sliding member. The sliding member engages the base member from its proximal end, whereafter the base member is secured to the horizontal portion of a mailbox post to provide a readily extendable and retractable assembly for improved access for postal service workers.