On 2011-08-02 21:59, Bruno Costacurta wrote:

Hello,

in my logs files there are messages 'connect from unknown[here an IP address]'.

Can this be considered be as probable spam ?

No.
It merely means that the machine connecting does not have forward confirmed reverse DNS (FCrDNS) entries. This occurs with home-based mail servers (who often cannot set their own PTR record), but even with larger company mail servers, where a pool of MXes don't all have their own hostname and/or IP.



And especially can Posfix blocked such connection ?

Certainly.

I tried to add the following :

smtpd_sender_restrictions =
  reject_unknown_sender_domain

Ýou mean *client*.
    smtp_client_restrictions = reject_unknown_client_hostname

NOTE that this is a very heavy restriction and will cause many, many false positives.

Instead, use the milder (but equally effective)
    smtp_client_restrictions = reject_unknown_reverse_client_hostname

This will reject all clients that do not have a PTR entry for their IP.

See http://www.postfix.org/postconf.5.html#smtpd_client_restrictions for the full list.

--
J.

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