Configuring Exim4 on Ubuntu

Exim4 is a message transfer agent (MTA) that can be used on Unix systems connected to the internet and can be installed in place of sendmail or Postfix.

Prerequisites

1. SMTP credentials of Mail relay servers (brevo or Amazon SES)

Installation

apt install exim4 -y

Configuration Steps via wizard

The dpkg-reconfigure exim4-config command opens a user interface to configure the exim4 mail agent.

1. Mail Server configuration type: Select mail sent by smarthost; received via SMTP or fetchmail.
2. Mail Name: Use system hostname.
3. IP Addresses to listen for incoming SMTP connections: 127.0.0.1.
4. Other Hostnames (or) Other Destinations: Use system hostname.
5. Mail relay machines: Leave this as blank.
6. IP Address or Hostname of SMTP Smarthost: Relay server IP address or Hostname with Port. (e.g., smtp-relay.brevo.com::587)
7. Hiding local mail name: Select Yes.
8. Visible domain name for local users:
   • Blank: Then the From Address will be user@hostname. (e.g., root@app-server-1)
   • example.com: Then the From Address will be root@example.com.
9. Dial-on-Demand: Select No.
10. Delivery method: Select mbox format in /var/mail/.
11. Split Configuration: Select No.

All configurable parameters from the user interface are stored in the /etc/exim4/update-exim4.conf.conf file. We can reconfigure the exim4 settings by re-running the wizard or manually wditing the file.

Resulting Configuration File

# /etc/exim4/update-exim4.conf.conf
#
# Edit this file and /etc/mailname by hand and execute update-exim4.conf
# yourself or use 'dpkg-reconfigure exim4-config'
#
# Please note that this is _not_ a dpkg-conffile and that automatic changes
# to this file might happen. The code handling this will honor your local
# changes, so this is usually fine, but will break local schemes that mess
# around with multiple versions of the file.
#
# update-exim4.conf uses this file to determine variable values to generate
# exim configuration macros for the configuration file.
#
# Most settings found in here do have corresponding questions in the
# Debconf configuration, but not all of them.
#
# This is a Debian specific file

dc_eximconfig_configtype='smarthost'
dc_other_hostnames='app-server-1'
dc_local_interfaces='127.0.0.1'
dc_readhost='example.com'
dc_relay_domains=''
dc_minimaldns='false'
dc_relay_nets=''
dc_smarthost='smtp-relay.brevo.com::587'
CFILEMODE='644'
dc_use_split_config='false'
dc_hide_mailname='true'
dc_mailname_in_oh='true'
dc_localdelivery='mail_spool'

Mail name is stored in /etc/mailname file.

root@app-server-1:~# cat /etc/mailname
app-server-1

SMTP Authentication

To configure the SMTP Authentication credentials, edit /etc/exim4/passwd.client file.

# Filename: /etc/exim4/passwd.client
# Purpose: Setup SMTP Credentials for exim4

# password file used when the local exim is authenticating to a remote
# host as a client.
#
# see exim4_passwd_client(5) for more documentation
#
# Example:
### target.mail.server.example:login:password

smtp-relay.brevo.com:12345678@smtp-brevo.com:password@123

Setting up /etc/aliases

The /etc/aliases file is used to create email aliases. To set up aliases for all users to include root and for root to include a Gmail address:

# /etc/aliases
mailer-daemon: postmaster
postmaster: root
nobody: root
hostmaster: root
usenet: root
news: root
webmaster: root
www: root
ftp: root
abuse: root
noc: root
security: root

root: sysadmin@example.com, example@gmail.com
monit: root