blocking outbound port 25 Home Page › Forums › Network Management › Firewall, Traffic Shaping and Net Balancer › blocking outbound port 25 This topic contains 3 replies, has 0 voices, and was last updated by ksrimoungchanh 8 years ago. Viewing 5 posts - 1 through 5 (of 5 total) Author Posts April 29, 2010 at 5:02 am #42379 ksrimoungchanhMember Hello All: I have my default ZS firewall policy on ACCEPT/Forward. It currently does not have any rules on it. Seems that all session initiated from within the lan is open. I am wanting to block all traffic from port 25 accept the mail server. What is the best implementation for this. I also have VOIP using SIP within the LAN that connects to a external SIP. I have tried to change the policy but it seems to mess this up when I do. Thank for any advice. Kou April 29, 2010 at 9:10 am #50238 ppaliasMember If traffic flows inside the LAN there not much you can do to block it. If the mail server is outside the LAN you can easily block access with a firewall rule. Do not change the policy, just create rules that BLOCK the traffic. April 29, 2010 at 1:27 pm #50239 ksrimoungchanhMember Hello ppalias, Thanks for the reply. I wanted to clarify myself on my initial email. I wanted to block all SMTP from within the LAN out to the INTERNET from all devices accept the internal Mail server. We caught a machine that was acting like it’s own email server and was possibly sending emails out from within the LAN out to the INTERNET without relaying it to our real mail server. is that still not possible? or with that information, there are some hopes. Kou April 29, 2010 at 4:39 pm #50240 ppaliasMember It is possible. Create first a rule to allow your mail server only and then a rule to block the whole subnet. Mind the sequence! Otherwise you will block everything! February 23, 2011 at 10:46 pm #50241 BrStevenMember Set up a rule on your firewall that blocks outbound TCP port 25, you can then use http://port25.icannotconnect.com to test if the rule is effective. Author Posts Viewing 5 posts - 1 through 5 (of 5 total) You must be logged in to reply to this topic.