Configuring your own mail server can be quite challenging. Even if you get the correct functionality you never know if you plugged all security holes. You can check this: https://workaround.org/ispmail/wheezy
. Most of it applies to Ubuntu as well.
I did it a few times and then installed Virtualmin. If you have only one domain, this is overkill, but it works perfectly. Setting up your complete web and mail hosting with a few mouse clicks. I know I am a whimpy but it made my life easy.
Virtualmin sets up Postfix, Dovecot and Roundcube.