apt-get install exim4

Set/adjust mail name as necessary:

vi /etc/mailname

Set aliases to redirect root mail to other email address:

vi /etc/aliases

add/amend

root: postmaster@example.com

apply new aliases file

newaliases

exim seems to use the local user (app-name) www-data without a domain as original sender which some email providers (e.g. emailantidote.com) rejects as valid sender.

Update exim config to set default domain for www-data user:

vi /etc/email-addresses

add

www-data: noreply@example.com

save and restart exim

/etc/init.d/exim4 restart

Now force mail queue:

exim -qff

To check the message queue, use

ls -la /var/spool/exim4/msglog/

To send via smarthost, generate a smarthost authentication file (replace with actual username/password):

echo "*:smarthost-login:smarthost-password" > /etc/exim4/passwd.client

By default, exim does not send external emails. Use the following to set it to send using “smarthost, no local” and ensure to enter the smart host name:

dpkg-reconfigure exim4-config

To allow non-tls passwords for the smarthost, use:

echo "AUTH_CLIENT_ALLOW_NOTLS_PASSWORDS = 1" >> /etc/exim4/exim4.conf.localmacros

To avoid 'message is too big (transport limit = 1)' error, triggered by some cron output, use:

echo "IGNORE_SMTP_LINE_LENGTH_LIMIT=1" >> /etc/exim4/exim4.conf.localmacros

Disable ipv6

sed -i s/dc_local_interfaces='127.0.0.1 ; ::1'/dc_local_interfaces='127.0.0.1'/g /etc/exim4/update-exim4.conf.conf
update-exim4.conf

Restart exim using

service exim4 restart