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From: "Gaby L" on 19 Apr 2010 11:31
Hi
I scan with my postfix server with NMap from other location.
The NMAP creats report smtp port open (It is OK) but apear Postfix smtpd and other information about MTA program.
I dont want to apear any information about my MTA server.

Thanks
Gaby
From: Wietse Venema on 19 Apr 2010 11:37
Gaby L:
> Hi
> I scan with my postfix server with NMap from other location.
> The NMAP creats report smtp port open (It is OK) but apear Postfix smtpd and other information about MTA program.
> I dont want to apear any information about my MTA server.

To disclose no information, close the SMTP port.

Seriously.

Even when you change the smtpd_banner value to say "$myhostname
ESMTP Sendmail" (this text MUST start with the hostname), the
server's replies (especially error messages) still reveal that it's
really Postfix.

Wietse

From: Linux Addict on 20 Apr 2010 13:23
On Mon, Apr 19, 2010 at 11:37 AM, Wietse Venema <wietse(a)porcupine.org>wrote:

> Gaby L:
> > Hi
> > I scan with my postfix server with NMap from other location.
> > The NMAP creats report smtp port open (It is OK) but apear Postfix smtpd
> and other information about MTA program.
> > I dont want to apear any information about my MTA server.
>
> To disclose no information, close the SMTP port.
>
> Seriously.
>
> Even when you change the smtpd_banner value to say "$myhostname
> ESMTP Sendmail" (this text MUST start with the hostname), the
> server's replies (especially error messages) still reveal that it's
> really Postfix.
>
> Wietse
>


Disclaimer :- It may violate some RFCs and possibly break the smtp system
itself.

[root(a)stick ~]# grep ^smtpd_banner /etc/postfix/main.cf
smtpd_banner = "unknown"

[root(a)stick ~]# telnet 0 25
Trying 0.0.0.0...
Connected to 0.
Escape character is '^]'.
220 "unknown"
From: Brian Evans - Postfix List on 20 Apr 2010 13:33
On 4/20/2010 1:23 PM, Linux Addict wrote:
>
>
> On Mon, Apr 19, 2010 at 11:37 AM, Wietse Venema <wietse(a)porcupine.org
> <mailto:wietse(a)porcupine.org>> wrote:
>
> Gaby L:
> > Hi
> > I scan with my postfix server with NMap from other location.
> > The NMAP creats report smtp port open (It is OK) but apear
> Postfix smtpd and other information about MTA program.
> > I dont want to apear any information about my MTA server.
>
> To disclose no information, close the SMTP port.
>
> Seriously.
>
> Even when you change the smtpd_banner value to say "$myhostname
> ESMTP Sendmail" (this text MUST start with the hostname), the
> server's replies (especially error messages) still reveal that it's
> really Postfix.
>
> Wietse
>
>
>
> Disclaimer :- It may violate some RFCs and possibly break the smtp
> system itself.
>
> [root(a)stick ~]# grep ^smtpd_banner /etc/postfix/main.cf <http://main.cf>
> smtpd_banner = "unknown"
>
> [root(a)stick ~]# telnet 0 25
> Trying 0.0.0.0...
> Connected to 0.
> Escape character is '^]'.
> 220 "unknown"
>
>

As Wietse mentioned, the above has no effect on determining the server type.

Just because the banner doesn't say Postfix, doesn't mean a
script/person couldn't figure it out from the response/error messages.

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