How to deny open relay internal SMTP? - OPENEMM 2015 R3

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How to deny open relay internal SMTP? - OPENEMM 2015 R3

Post by ikom » Thu Apr 06, 2017 11:09 am

Hi guys,
I'm doing the setup of OPENEMM 2015 R3 following the official guide: OpenEMM-2015_InstallAdminGuide_1.3.2.pdf
I've noticed an issue related to the internal smtp, when I test it for the open relay on the major sites, it fails.
Trying to test it via telnet I get this behaviour:

Code: Select all

telnet 25
Connected to
Escape character is '^]'.
220 Python SMTP proxy version 0.2
mail from:<> 
250 Ok
rcpt to:<>
250 Ok
354 End data with <CR><LF>.<CR><LF>
bounce relay test
250 Ok
Actually the email it isn't sent to John, but Jane receive the bounce:

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Subject: Mail failed: 510 Unknown user
Mail failed due to 510:
Unknown user

The original message follows:
> Return-Path: <>
> From:
> X-AGNLoop: set
bounce relay test
This issue makes the internal smtp not usable in a production environment with 25 port open.
In the very few minutes that I spent to doing this test, I see in the mail log unexpected bounces to unknown email addresses (foreign connections).
There is a way to deny the relay at the RCPT TO: stage with the internal SMTP as other sendmail instances do? (550 5.7.1 <>... Relaying denied)

I tried to search in the forum similar topic but I only found this: ... c1312.html
It's similar to my question but there is no solution at openemm software level and it not consider the bounce that is actually sent.

Any thoughts and suggestions to resolve this issue are kindly appreciated, thank you.