The ornamental design for a wall-mount mailbox, as shown and described.
FIG. 1 is a front perspective view of a wall-mount mailbox showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The dotted lines in the drawings form no part of the claimed design, but are shown to help illustrate an environment in which the claimed design may be used.