Games like The Mailman
Games like The Mailman include Portal 2, Five Nights at Freddy's: Security Breach, Portal, SUPERHOT, and Resident Evil Requiem. We matched them by the tags players give The Mailman on Steam (Action, Puzzle, FPS, 3D, and Colorful): closest matches first, and among equally close ones the better-known games.

Portal 2
Shared: Puzzle · First-Person · Funny

Five Nights at Freddy's: Security Breach
Shared: Horror · First-Person · 3D

Portal
Shared: Puzzle · First-Person · Action

SUPERHOT
Shared: Action · FPS · Puzzle

Resident Evil Requiem
Shared: Action · FPS · Horror

Half-Life 2
Shared: Action · FPS · First-Person

Superliminal
Shared: Puzzle · First-Person · Thriller

Poppy Playtime
Shared: Puzzle · Horror · First-Person

Shotgun Farmers
Shared: Action · FPS · First-Person

Buckshot Roulette
Shared: First-Person · Horror · 3D

Atomic Heart
Shared: Action · FPS · Puzzle

Black Mesa
Shared: Action · FPS · First-Person

R.E.P.O.
Shared: Horror · 3D · First-Person

Blood and Bacon
Shared: Action · FPS · Funny

BONEWORKS
Shared: Action · Puzzle · First-Person

VLADiK BRUTAL
Shared: FPS · Action · First-Person

Bendy and the Ink Machine
Shared: Puzzle · First-Person · Horror

Ravenfield
Shared: FPS · Action · First-Person

DOOM
Shared: Action · FPS · First-Person

Garry's Mod
Shared: Funny · FPS · First-Person

Garten of Banban
Shared: Puzzle · First-Person · Horror

Ready or Not
Shared: FPS · Action · First-Person

Paper Dolls: Original /
Shared: Action · Puzzle · Horror

ParanormalHK
Shared: Horror · Puzzle · Funny