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Use this for personal machines behind someone else's LAN. It turns exim into a MUA instead of a MTA. That is, tt uses your remote self-hosted smtp instead of sending directly.
sudo apt install exim4 sudo nano /etc/exim4/update-exim4.conf.conf dc_eximconfig_configtype='smarthost' dc_smarthost='mail.domain.com::587' dc_local_interfaces='127.0.0.1 ; ::1' dc_other_hostnames='' dc_readhost='haacksnetworking.org' dc_relay_domains='' dc_minimaldns='false' dc_hide_mailname='true' #just in case dc_localdelivery='notifications@haacksnetworking.org' sudo nano /etc/exim4/passwd.client mail.domain.com:user:password *:user:password sudo chown root:Debian-exim /etc/exim4/passwd.client sudo chmod 640 /etc/exim4/passwd.client #setup headers sudo nano /etc/email-addresses sexa: remote@haacksnetworking.org root: remote@haacksnetworking.org *: remote@haacksnetworking.org #calm tls sudo nano /etc/exim4/exim4.conf.localmacros MAIN_TLS_ADVERTISE_HOSTS = REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS = * MAIN_HARDCODE_PRIMARY_HOSTNAME = domain.com MAIN_LOCAL_DOMAINS = #disable_ipv6=true #if needed sudo update-exim4.conf sudo systemctl restart exim4 echo "Test after permission fix" | mail -s "Exim4 test 2" oemb1905@jonathanhaack.com sudo tail -f /var/log/exim4/mainlog
Here's a copy pastable version:
sudo apt install exim4 cat << 'EOF' | sudo tee /etc/exim4/update-exim4.conf.conf dc_eximconfig_configtype='smarthost' dc_smarthost='mail.domain.com::587' dc_local_interfaces='127.0.0.1 ; ::1' dc_other_hostnames='' dc_readhost='haacksnetworking.org' dc_relay_domains='' dc_minimaldns='false' dc_hide_mailname='true' dc_localdelivery='notifications@haacksnetworking.org' EOF cat << 'EOF' | sudo tee /etc/exim4/passwd.client mail.domain.com:user:password *:user:password EOF sudo chown root:Debian-exim /etc/exim4/passwd.client sudo chmod 640 /etc/exim4/passwd.client sudo cat << EOF > /etc/email-addresses sexa: remote@haacksnetworking.org root: remote@haacksnetworking.org *: remote@haacksnetworking.org EOF cat << 'EOF' | sudo tee /etc/exim4/exim4.conf.localmacros MAIN_TLS_ADVERTISE_HOSTS = REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS = * MAIN_HARDCODE_PRIMARY_HOSTNAME = domain.com MAIN_LOCAL_DOMAINS = #disable_ipv6=true #if needed EOF sudo update-exim4.conf sudo systemctl restart exim4 echo "Exim4 configured and restarted." echo "Test with:" echo 'echo "Test from $(hostname)" | mail -s "Exim4 test from $(hostname)" test@gmail.com'
We turned off local delivery above so now all we need to do is set the hostname and mailname to domain.com:
echo "haacksnetworking.org" | sudo tee /etc/mailname echo "haacksnetworking.org" | sudo tee /etc/hostname
Then, in /etc/hosts enter something like:
127.0.1.1 domain.com domain
Send a few test emails to external domains (external to mail server) and to local users (local on the client):
echo "Satellite test $(date)" | mail -s "Normal satellite test 7" root echo "Satellite test $(date)" | mail -s "Normal satellite test 7" oemb1905@gmail.com
Alias Test
Both will work … and here's how and why. In the first case, you send from the client to root, and exim sends the email (via the above configuration) to the address root@</etc/mailname>. Since the client's mailname is domain.com, and since root@domain.com exists on the remote email server, the client sends to that address. And, in my case, the email server's root address is aliased to notifications@domain.com, and the email arrives. Moreover, since the mail server recognizes that the email it is sending is going to a local user, spf is bypassed since it is trusted. DKIM still works.
External Test
— oemb1905 2026/04/08 16:04
