topic SMTP PROBLEM in Network Security

SMTP PROBLEM

soumik1979 — Mon, 11 Mar 2019 18:43:37 GMT

Dear all

i am a network administrator of a small comp.Today we have faced a strange Problem

Internet leased line------------ Router---- catalystswitch -----External Servers and IP devices

| |

Cyberoam UTM |

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Lan internet and mail users |

ASA 5510

Lan high end users and servers internet access

Every thing was working fine.But today I fond that our mail users are unable to send mail.They can receive mail, but unable to send.I checked that telnet mail.domainname.com 25 was not connecting from any of the lan users who have gateway as asa 55510 Ip or cyberoam IP.But when I telnet from a external server, it was working.No conf change was done recently.Some how both of my firewalls deny the smtp traffic.Can any body help me regarding that.

Please help me .If you want any more feedback plz let me know.

Re: SMTP PROBLEM

mirober2 — Wed, 22 Sep 2010 16:49:55 GMT

Hello,

If the ASA is blocking the traffic, you can check the syslogs to find out the reason. You can also use the packet-tracer command to see why the traffic would be dropped:

packet-tracer in inside tcp 12345 25

Interface and ASP drop captures on the ASA may also help you see why the connection is failing. Here is a guide that describes how to setup captures on the ASA:

https://supportforums.cisco.com/docs/DOC-1222

Hope that helps.

-Mike

Re: SMTP PROBLEM

nseshan — Thu, 23 Sep 2010 17:07:41 GMT

As Mike has rightly pointed out, that you need to apply packet captures to actually check whether the traffic for port 25 is reaching the firewall itself from the internal LAN. If it is, the you need to apply captures on the external interface to check if it is leaving the firewall. Also, we could check if you firewall is inspecting smtp traffic and whether the inspection is causing issues. To check this, you can issue the command "sh run policy-map" and "sh service-policy". It would be good if you could attach those outputs to this string.