[Dovecot] adding new user to dovecot

[Sven Kirmess]

"Normally" you would have one system user account for each mail user.
The mail user would be the system account. Therefore, you would create
a user kartik (any other name is fine too). The mails would be stored
in the home directory of this user (normally, this would be /home/kartik).
This is all configurable...

As Johannes already pointed out, ~ is a synonym for the home directory of
the current user in a shell. If you, as user kartik, type:
kartik> echo ~
you get the answer
/home/kartik
which is the home directory of user kartik. You can use ~kartik or ~root or
anything else and this always resolves to the home directory of the specified
  user.

Maybe you should tell us what you would like to do. Operating system,
number of users, existing solution...

Sven