Depends where you work.
My last job you had to lock it, of some wag would email the entire company confessing, in your name, to fucking hamsters, here it's fine, everyone's professional and most of them fear me.
( CQ Knows the truth, all of it., Mon 7 Nov 2011, 15:48, 2 replies, latest was 14 years ago)

nothing confidential here, not very professional at all really

(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Mon 7 Nov 2011, 15:51, Reply)

most mental asylums are a bit like that, i hear

( rachelswipe with a fork, Mon 7 Nov 2011, 15:54, Reply)

yeah, you should see the abuse that goes on
the other day it took 6 orderlys to stop me from raping taht one guy
(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Mon 7 Nov 2011, 15:58, Reply)

On the spot sackable offence to give someone your password for us.
Same if someone sent an abusive email from your computer. Your PC, your responsibility.
( Davros' Granddad a voice of calm reason in a world of spastics., Mon 7 Nov 2011, 15:54, Reply)