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,...
Exchange Error 451 4.4.0 primary target IP address responded with…
KB ID 0000252 Problem You see this error message on your Exchange outbound queues. 451 4.4.0 primary target IP address responded with “421.4.4.2 unable to connect.”attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. Solution Essentially this is a communication error, you can’t connect to the other end on TCP port 25 (SMTP)....