hostname does not resolve to address warning

[Eugene Podshivalov]

Hi all,

I have the following config

smtpd_client_restrictions =
    reject_unknown_client_hostname
smtpd_helo_required = yes
smtpd_helo_restrictions =
    reject_invalid_helo_hostname,
    reject_non_fqdn_helo_hostname,
    reject_unknown_helo_hostname
smtpd_sender_restrictions =
    reject_non_fqdn_sender,
    reject_unknown_sender_domain

but still get warnings like this

postfix/smtpd[24986]: warning: hostname server17-ams1.internet-census.org does not resolve to address 107.6.163.34: Name or service not known
postfix/smtpd[24986]: connect from unknown[107.6.163.34]
postfix/smtpd[24986]: NOQUEUE: reject: CONNECT from unknown[107.6.163.34]: 450 4.7.25 Client host rejected: cannot find your hostname, [107.6.163.34]; proto=SMTP
postfix/smtpd[24986]: disconnect from unknown[107.6.163.34] ehlo=0/1 quit=1 commands=1/2

My understanding is that there should be no warning because the issue is explicitly checked by the "reject_unknown_client_hostname" directive.

Am I missing something? Is it possible to eliminate this warning?

Thanks

Без вирусов. www.avast.ru

[Wietse Venema]

Eugene Podshivalov:

> Hi all,
> I have the following config
>
> > smtpd_client_restrictions =
> >     reject_unknown_client_hostname
> > smtpd_helo_required = yes
> > smtpd_helo_restrictions =
> >     reject_invalid_helo_hostname,
> >     reject_non_fqdn_helo_hostname,
> >     reject_unknown_helo_hostname
> > smtpd_sender_restrictions =
> >     reject_non_fqdn_sender,
> >     reject_unknown_sender_domain
>
>
> but still get warnings like this
>
> > postfix/smtpd[24986]: warning: hostname server17-ams1.internet-census.org
> > does not resolve to address 107.6.163.34: Name or service not known
> > postfix/smtpd[24986]: connect from unknown[107.6.163.34]
> > postfix/smtpd[24986]: NOQUEUE: reject: CONNECT from unknown[107.6.163.34]:
> > 450 4.7.25 Client host rejected: cannot find your hostname, [107.6.163.34];
> > proto=SMTP
> > postfix/smtpd[24986]: disconnect from unknown[107.6.163.34] ehlo=0/1
> > quit=1 commands=1/2

Postfix logs this warning, so that you can understand WHY a client
may be rejected with reject_unknown_client_hostname, and how the
problem may be fixed.

1 - A problem with the address->name mapping (lookup failed)

2 - A problem with the address->name mapping (the mapping does not
    exist).

3 - A problem with the name->address mapping (lookup failed)

4 - A problem with the name->address mapping (the mapping does not
    exist)

5 - A problem with the name->address mapping (the mapping does not
    match the client IP address)

In your case the probkem was #4.

        Wietse

[Eugene Podshivalov]

 Thanks for the reply.

The warning says that "hostname does not resolve to address" (case #4) but then the log says that connection is rejected because it cannot find a hostname (case #2).

So which one is the actual rejection reason? Doesn't it feel a bit confusing?

Regards

Без вирусов. www.avast.ru

пн, 23 нояб. 2020 г. в 17:40, Wietse Venema <[hidden email]>:

Eugene Podshivalov:
> Hi all,
> I have the following config
>
> > smtpd_client_restrictions =
> >     reject_unknown_client_hostname
> > smtpd_helo_required = yes
> > smtpd_helo_restrictions =
> >     reject_invalid_helo_hostname,
> >     reject_non_fqdn_helo_hostname,
> >     reject_unknown_helo_hostname
> > smtpd_sender_restrictions =
> >     reject_non_fqdn_sender,
> >     reject_unknown_sender_domain
>
>
> but still get warnings like this
>
> > postfix/smtpd[24986]: warning: hostname server17-ams1.internet-census.org
> > does not resolve to address 107.6.163.34: Name or service not known
> > postfix/smtpd[24986]: connect from unknown[107.6.163.34]
> > postfix/smtpd[24986]: NOQUEUE: reject: CONNECT from unknown[107.6.163.34]:
> > 450 4.7.25 Client host rejected: cannot find your hostname, [107.6.163.34];
> > proto=SMTP
> > postfix/smtpd[24986]: disconnect from unknown[107.6.163.34] ehlo=0/1
> > quit=1 commands=1/2

Postfix logs this warning, so that you can understand WHY a client
may be rejected with reject_unknown_client_hostname, and how the
problem may be fixed.

1 - A problem with the address->name mapping (lookup failed)

2 - A problem with the address->name mapping (the mapping does not
    exist).

3 - A problem with the name->address mapping (lookup failed)

4 - A problem with the name->address mapping (the mapping does not
    exist)

5 - A problem with the name->address mapping (the mapping does not
    match the client IP address)

In your case the probkem was #4.

        Wietse

[Wietse Venema]

> postfix/smtpd[24986]: warning: hostname server17-ams1.internet-census.org
> does not resolve to address 107.6.163.34: Name or service not known

This is a type 4 error (the name->address mapping does not exist).

> postfix/smtpd[24986]: connect from unknown[107.6.163.34]
> postfix/smtpd[24986]: NOQUEUE: reject: CONNECT from unknown[107.6.163.34]:
> 450 4.7.25 Client host rejected: cannot find your hostname, 107.6.163.34];

Postfix was unable to determine the remote SMTP client hostname.
This error message is sent to the remote SMTP client. Error details
are not made available to the remote SMTP client. Error details are
logged only. Then, the local system administrator can deal with it.

        Wietse