Setup Exim to Send Email Using Gmail in Debian

Install Exim4

apt-get install exim4

Configuration

Run following command to configure Exim4.

dpkg-reconfigure exim4-config

Choose this option when asked: "mail sent by smarthost; no local mail".
Fill in the rest of the fields:

System mail name: YOUR_HOSTNAME
IP-addresses to listen on for incoming SMTP connections: 127.0.0.1 ; ::1
Other destinations for which mail is accepted: <BLANK>
Visible domain name for local users: <BLANK>
IP address or host name of the outgoing smarthost: smtp.gmail.com::587
Keep number of DNS-queries minimal (Dial-on-Demand)? No
Split configuration into small files? No
Root and postmaster mail recipient: <BLANK>

Open and edit /etc/exim4/exim4.conf.template.
Search for:

.ifdef DCconfig_smarthost DCconfig_satellite

Then add these lines after it:

send_via_gmail:
    driver = manualroute
    domains = ! +local_domains
    transport = gmail_smtp
    route_list = * smtp.gmail.com

Remove other smarthost blocks that contains domains = ! +local_domains.
Search for:

begin authenticators

And add these lines after it:

gmail_login:
    driver = plaintext
    public_name = LOGIN
    client_send = : YOUR_GMAIL_ACCOUNT@gmail.com : YOUR_GMAIL_PASSWORD

Remove other authenticator blocks that contains public_name = LOGIN.
Search for:

transport/30_exim4-config_remote_smtp_smarthost

And add these lines after it:

gmail_smtp:
    driver = smtp
    port = 587
    hosts_require_auth = $host_address
    hosts_require_tls = $host_address

Save and close /etc/exim4/exim4.conf.template.
Apply the new configuration:

update-exim4.conf

Restart Exim4 service:

/etc/init.d/exim4 restart

Testing

Now send a test email using following command:

echo 'Test Message from VULTR.' | mail -s 'Test Message' YOUR_EMAIL_ADDRESS

Check /var/log/exim4/mainlog if any errors occurred.