# First, let's create a directory for the jail account
mkdir /jail
chown root:root /jail

# Then we create a new user account specially for jail account
# *replace <group name>, <username>, <password> with your own value
groupadd <group name>
useradd -d /home/jail -g <group name> -p <password> <username>

# For example, if we only want to allow the jail account to have ssh and basic shell access
jk_init -v -j /jail basicshell ssh

# Then we shall jail the user account we previously created to the jail directory
jk_jailuser -m -j /jail <username>

Now the jail account and file system is ready, however if you want more control, we can do the following.

# OPTIONAL: Edit /jail/etc/passwd file and /jail/etc/group file to further limit the access
# The following further limit the user logged in jail account to have only access to bash
# Assume the jail user account & group = jail_user, and we edit the passwd file
jail_user:x:1016:1016:/home/jail:/bin/bash

# edit group file
jail_user:x:1016

First, we have to install “postfix” as the MTA and “mailx” as the mail utility.

sudo apt-get install postfix
sudo apt-get install mailx

Then, we will create a user on ubuntu as the mail user account

sudo useradd -m -s /bin/bash <username>
sudo passwd <username>

Now, the first step is done, and we might have a test on it by issuing

netcat localhost 25

and it should prompt you with this

220 localhost ESMTP Postfix (Ubuntu)

Next, we shall setup the “Maildir” mailboxes for the sake of scalability, this is preferred over the “mbox” mailbox

sudo postconf -e "home_mailbox = Maildir/"
sudo postconf -e "mailbox_command = "

## restart the postfix
sudo /etc/init.d/postfix restart

Now, the setup of postfix is done, and we should move to MDA, and here I have chosen to use “Dovecot” since this is the first MDA I tried and i am used to it. (*note: this install both IMAP and POP3, and you might only install either one of them in case)

sudo apt-get install dovecot-imapd dovecot-pop3d

Open up /etc/dovecot/dovecot.conf, and make sure the following setting is made

protocols = pop3 pop3s imap imaps
pop3_uidl_format = %08Xu%08Xv

## to allow remote access
listen = *

## only set it to no, if the server is to be used with virtual account or internally, else ignore this setting
disable_plaintext_auth = no

mail_location = maildir:/home/%u/Maildir

Then start up the dovecot

/etc/init.d/dovecot start

Up to this moment, the mail server is ready, however if you need SSL support and thunderbird support, read the rest.
To be able to make use of SSL, you need to generate a key and certificate through openSSL, and can be referred to this previous article.
After the key and certificate is ready, set it as follow inside the /etc/dovecot/dovecot.conf

ssl_cert_file = /etc/ssl/certs/<certificate file>.crt
ssl_key_file = /etc/ssl/private/<key file>.key
ssl_disable = no

Finally, to allow thunderbird client to connect to the mail server, modify /etc/dovecot/dovecot.conf as follows:

protocol imap {
...
login_greeting_capability = yes
imap_client_workarounds = tb-extra-mailbox-sep
}

Reference: Postfix How-To Dovecot

1. Extracting IP of the current machine

ifconfig | grep 'inet addr:' | grep -v '127.0.0.1' | cut -d: -f2 | awk '{print $1}'

2. Getting the Gateway of the current machine

route -n | grep 'UG[ \t]' | awk '{print $2}'

3. Updating the network settings

// ifconfig <network interface> <ip> netmask <subnetmask> broadcast <broadcast address>
ifconfig eth0 192.168.0.10 netmask 255.255.255.0 broadcast 192.168.0.255

4. Updating Gateway

// in order to achieve this, we need to first delete the
// existing gateway entry and then add the new one
route del default

// route add -net default gw <gateway address> netmask 0.0.0.0 dev eth0;
route add -net default gw 192.168.0.255 netmask 0.0.0.0 dev eth0