Allow insecure connections to POP3 / IMAP iRedMail

In order to be able to connect to POP3 / IMAP without STARTTLS, you need to open the Dovecot configuration file:

sudo nano /etc/dovecot/dovecot.conf

Edit the two parameters listed below:


To return the parameters of the secure connection to POP3S / IMAPS back:


After the changes in the Dovecot configuration, you need to restart it:

sudo /etc/init.d/dovecot restart

See also:
How to enable SMTP without SSL on port 25 in iRedMail / Postfix

Ubuntu IP Masquerading (NAT)

For example, I will configure IPv4 masquerading (NAT) on Ubuntu Server.
First you need to enable packet forwarding in /etc/sysctl.conf so that traffic can walk between different network interfaces.
Let’s check the current status:

sysctl net.ipv4.conf.all.forwarding
cat /proc/sys/net/ipv4/ip_forward

If it is 0, then enable it with the following command:

sysctl -w net.ipv4.conf.all.forwarding=1

To keep this after the system restart, open the file /etc/sysctl.conf for example in the nano editor (Ctrl + X to exit, y / n to save or discard changes):

nano /etc/sysctl.conf

And add the line:


If necessary, you can clear existing NAT rules:

iptables -t nat --flush

Now it remains to add a rule to iptables, for example:

iptables -t nat -A POSTROUTING -s -j SNAT --to-source

Where, internal network, and the address through which you need to go to the Internet, similarly prescribed other internal networks.
Let me remind the mask for private networks:

If the IP address on the external network interface changes (dynamic), then instead of SNAT we specify MASQUERADE:

iptables -t nat -A POSTROUTING -s -j MASQUERADE

Do not forget to save the added iptables rules.
For example, you can open the network interface configuration file (its contents are loaded at system startup):

nano /etc/network/interfaces

And at the end add iptables rules, for example I will indicate the masquerading of this network at once to several IP addresses, and also with the indication of the network interface:

post-up /sbin/iptables -t nat -A POSTROUTING -s -o eth3 -j SNAT --to-source --persistent

Or add to the file:

nano /etc/rc.local
/sbin/iptables -t nat -A POSTROUTING -s -o eth3 -j SNAT --to-source --persistent

I recommend to specify the outgoing network interface, if you do not specify it, then local traffic will return to the network under NAT IP.
If there are several outgoing interfaces, let’s say the load is balanced through BGP, etc., then we indicate with two rules:

/sbin/iptables -t nat -A POSTROUTING -s -o eth3 -j SNAT --to-source --persistent
/sbin/iptables -t nat -A POSTROUTING -s -o eth4 -j SNAT --to-source --persistent

See also my articles:
Difference between MASQUERADE and SNAT
Configuring IPTables
How to fix the error “nf_conntrack: table full, dropping package”
Using Linux ISG

Installing ISC DHCP for ABillS

Here is an example of the installation of the ISC DHCP server for ABillS in Ubuntu Server.

Switch to the root user:

sudo su

Install package:

apt-get install isc-dhcp-server
ln -s /usr/abills/Abills/modules/Dhcphosts/ /usr/abills/libexec/


/usr/abills/libexec/ -d LEASES=/var/lib/dhcp/dhcpd.leases

Change owner of a file:

chown www-data /etc/dhcp/dhcpd.conf

Open the in the Editor:

nano /usr/abills/libexec/

Add options:

$conf{DHCPHOSTS_RECONFIGURE}='/usr/bin/sudo /etc/init.d/isc-dhcp-server restart';

Open in the Editor:

nano /etc/sudoers

Add the string making the ability to run a service system:

www-data   ALL = NOPASSWD: /etc/init.d/isc-dhcp-server

Go to the Abills Web interface, open the menu "settings"-"IP (DHCP)"-"Network IP (DHCP) Network", add the network if needed, then "Show, reconfigure the dhcp" and "Reconfigure".

See if the isc-dhcp-server command:

/etc/init.d/isc-dhcp-server status

Logs are written to the file/var/log/syslog

You can also configure the export of DHCP history to see it in the “Report” – “DHCP History” menu.
To do this, make a link:

ln -s /usr/abills/Abills/modules/Dhcphosts/ /usr/abills/libexec/

Separating DHCP logs into a separate file as I wrote in the article below and adding to the Startup script with the command:

tail -F /var/log/dhcpd.log | /usr/abills/libexec/

See also my articles:
Installing and configuring a dhcp server, isc-in Ubuntu
Packet capturing with tcpdump