The ornamental design for a multi-sectional door for a flex rackserver, as shown and described.
FIG. 1 is a front perspective view of a multi-sectional door for a flex rack server with stacked middle and bottom sections;
FIG. 2 is a front view thereof;
FIG. 3 is a side view thereof; and,
FIG. 4 is an enlarged top view thereof.
Broken lines shown in the drawings illustrate portions of the housing of the multi-sectional door for a flex rack server and form no part of the claimed design.