Configuring exim4 as a Mail Relay on Ubuntu Linux

My goal is to have the system’s MTA (exim4) forward any emails sent on the local host to a remote mail server for distribution. No mail will be received locally on this host, all mail will be forwarded elsewhere.

Ubuntu uses the command dpgk-reconfigure exim4-config to generate the exim4 configuration file /var/lib/exim4/config.autogenerated. Two additional files must be created to complete the configuration.

1. Create /etc/exim4/exim4.conf.localmacros containing the line:
   MAIN_LOCAL_DOMAINS =
   This will force exim4 to send all mail to the remote mail server and not to try to delivery anything locally.
2. Edit /etc/exim4/passwd.client and add a line containing the SMTP login used to access the remote mail server:
   *:userid:password
   Beware that special characters in the userid or password can cause problems.
3. Run dpgk-reconfigure exim4-config
   • General type of mail configuration: mail sent by smarthost; no local mail
   • System mail name: your_hostname.com
   • IP-address to listen on for incoming SMTP connections:127.0.0.1 ; ::1
   • Other destinations for which mail is accepted: leave this blank
   • Visible domain name for local users: your_hostname.com
   • IP address or host name of the outgoing smarthost: mail.server.com::587
   • Keep number of DNS-queries minimal (Dial-on-Demand)? No
   • Split configuration file into small files? No
4. Restart exim4: systemctl restart exim4