I claim the ornamental design for a mailing envelope, as shown and described.
FIG. 1 is a perspective view of a mailing envelope, illustrated in an unsealed configuration, showing my new design;
FIG. 2 is a front elevational view thereof, illustrated in the unsealed configuration with a suspension loop exposed;
FIG. 3 is a rear elevational view thereof, illustrated in the sealed configuration;
FIG. 4 is a left-side elevational view thereof, illustrated in a sealed configuration with the suspension loop hidden;
FIG. 5 is a right-side elevational view thereof, illustrated in the sealed configuration;
FIG. 6 is a top plan view thereof, illustrated in the sealed configuration;
FIG. 7 is a bottom plan view thereof, illustrated in the sealed configuration; and,
FIG. 8 is an alternate perspective view thereof, illustrated in the sealed configuration.
The broken line showing of the mailing label in FIG. 8 is included for the purpose of illustrating use and environment and forms no part of the claimed design.