Assuming this is not hosted on your home system, since ISPs may block the ports and also most of the dynamic ips allocated are blacklisted, the issue with postfix is that its difficult to have a single set and forget config if you intend to use it on multiple internal machines, like for getting your root email on each system to one mailbox. Ideally you want a single main.cf for all your internal machines and for the outgoing/incoming mailhost to be determined solely by your mx or internal dns alias, but this is next to impossible with a single postfix config without getting mail loops on the system that is the mailhost. Exim and sendmail at least separate out the submit config from the rest of the configuration. Also you would be insane to try this without fail2ban or something similar. Postfix does a reasonable job of handling attackers but it does so quietly -- so you may not see the activity.