replyable 

A tool, that the user has a long history with, which always gets the job done.

the one side character that everyone hated at first but later on the main character's nephew calls him a reliable guy and ends up being the only character he's ever really said that too

There is email, there is spam and then there is replyall.
Replyall is internal spam.
Replyall is the slop that fills your inbox from co-workers needing reassurance about their contribution. Replyall is what happens when people don't think about who needs the information they are providing in response to a legitimate question or action.

A source that you can trust. Someone that you know is telling the truth and you can depend on.

Instead of saying “Sorry, I don’t know how to reply” cut it short to repliable smh