Cisco ASA – Only Allow Mail Servers SMTP Outbound
KB ID 0000172 Problem It’s not unusual for nasty Virus’s and Malware once they have infected a machine, to set up outbound communications on the mail protocol SMTP (TCP Port 25), which can lead to your public address being blacklisted. So it’s considered good practice to stop all your clients getting mail access outbound through your firewall, while still allowing your mail server. Note: On Cisco firewall’s,...