Getting "Unexpected failure, please try later" error

If you encounter "Unexpected failure, please try later" error when sending mail out, the first thing to check is /opt/afterlogic/var/log/exim/eximmain.log file. It may contain the following records:

failed to open /opt/afterlogic/etc/exim/sender_local_domain.list when checking "/opt/afterlogic/etc/exim/sender_local_domain.list": No such file or directory

Should that be the case, please try running the following commands:

mkdir -p /opt/afterlogic/lib/exim/lookups/
mkdir -p /opt/afterlogic/etc/exim/
touch /opt/afterlogic/etc/exim/sender_local_domain.list

For both the directories created, adjust access permissions recursively:

chown afterlogic:afterlogic -R /opt/afterlogic/etc/exim
chown afterlogic:afterlogic -R /opt/afterlogic/lib/exim

And restart the service with:

sudo service exim4 restart