Fatal! Write failure for /etc/valiases/..

When adding an email forwarder you may see an error like this:
Fatal! Write Failure: /etc/valiases/thecpaneladmin.com. Ignore any messages of success this can only result in failure!
To fix this, run (replace user with username and domain with the domain name)

chown user:mail /etc/valiases/domain.com
chmod 644 /etc/valiases/domain.com