Can not write to /etc/valiases

A typical error will look as follows:

fatal! Write Failure: /etc/valiases/. Ignore any messages of success this can only result in failure!

Generally the permissions on the file /etc/valiases/domain.com are incorrect. You can fix this by running

chown username:mail /etc/valiases/domain.com

Another option is to run the cpanel script /scripts/fixvaliases. This will reset all the permissions for each file in /etc/valiases.