In a larger organisation the main firewall will be carefully fine tuned to only allow outbound connections to the internet under control.
However, one of my clients is behind a relatively simple BT Home Hub which doesn't offer much in terms of outbound firewall connectivity - and they have a pretty unmanaged Windows 2012 server sat on their LAN. I was surprised (well not that surprised) to learn that the default on Windows 2012 firewall outbound is to allow all outbound traffic. I'd always assumed that because there are a whole block of enabled outbound rules sat there that only the ports/programs configured in those rules have access. I was perplexed how I was able to telnet to their ISP's SMTP server without an obvious rule allowing it. Change the default behaviour to block briefly and yes, lost telnet to port 25.
My question is it safe to change the default to block and will Windows and other programs have added the required outbound rules or do I face spending quite a while adding custom rules?
I tempted to suggest we find a good value firewall that does allow outbound rules to be controlled.