I just read another answer here, with another config item. To replicate, I used the following:
mkdir -p /etc/e-smith/templates-custom/etc/main.cfg echo # reject_non_fqdn_helo_hostname, # reject_invalid_helo_hostname, > /etc/e-smith/templates-custom/etc/main.cfg
But, would this not just add another entry to the file as it’s not really appending another line? (I am not even sure this is the correct method).