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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=''
dc_relay_domains=''
dc_minimaldns='false'
dc_hide_mailname='true'

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 = user.domain.com
MAIN_LOCAL_DOMAINS =


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=''
dc_relay_domains=''
dc_minimaldns='false'
dc_hide_mailname='true'
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 = user.domain.com
MAIN_LOCAL_DOMAINS =
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'

For system alerts/errors, the system will attempt to email root@mailname, so we also need to change /etc/mailname to the top level domain.

echo "haacksnetworking.org" | sudo tee /etc/mailname

Once that's done, edit /etc/aliases so that messages to root get sent to your target email address and use the domain user + domain specified above:

root: notifications@haacksnetworking.org

Simulate a local error and see if it arrives properly:

echo "System Error Send Test - $(date)" | mail -s "System Error Send Test $(date)" root

If everything is setup right, the email should arrive at notifications@haacksnetworking.org. Now, for spf to pass, you have two approaches:

1. Make the client think it is domain.com by changing hosts and hostname like you did mailname
2. Create a subdomain record for client.domain.com that permits the mailserver as an origin

The reason this is needed is because of the sender's envelope domain showing as client.domain.com in the headers to target email servers. Theoretically, the changes in /etc/email-addresses should handle this, but I found that they did not do that reliably. This should resolve that issue.

— oemb1905 2026/04/08 16:04