The Mailroom endless mode how to unlock has two answers: finish the campaign, which means completing the whole game, or switch it on yourself in the options settings without finishing anything first. Either route gets you the same mode, where the sorting never stops.
The Mailroom endless mode how to unlock: the two ways in
There are two ways in:
- Finish an entire shift, which is completing the game.
- Turn the mode on yourself in the options settings.
The second route exists so you do not have to replay the campaign to see the mode, and it is the switch to look for if you are checking it out before you have finished the story.
What endless mode changes
In endless mode you never leave the mailroom. You keep sorting forever, and each stretch of play brings something new to deal with, which is what keeps the late game fresh. The mode's own description is deliberately bleak about it: you will be here forever and ever and ever.
The story campaign itself is fairly short, so endless mode is where the game keeps offering new material after the ending, and where the remaining questions about the building can still be dug into. The campaign does not end on a victory screen either: the last sequence leaves you inside the building, and the ending is deliberately open rather than conclusive, with a lot of the building left unexplained. What that ending looks like, and why the last sequence leaves you inside the building rather than out of it, is covered in hell's exit and the locked door.