A friend of mine (we'll call him "Jeff") one time guessed his friend's ("Greg") voicemail password and was listening to the guy's messages for about a year before he finally told him.
Greg was so pissed with Jeff that he walked out of the house and started to drive away. Greg had to physically throw himself in front of the car to keep Jeff from leaving.
It took Greg a LONG time to get past it.
So if you happen to acquire a friend's email password, my recommendation is to:
- Tell him about it so he can change his password, or
- Forget about it.
But under no circumstances should you violate your friend's privacy. After all, if your friend discovered your email password, you wouldn't want him looking at your email.