Nicolas Kovacs writes:
> Hi,
>
> I'm running our local school's mail server on CentOS 7, Postfix and
> Dovecot. We get quite a lot of spam, so I have the following sender
> restrictions in my /etc/postfix/main.cf:
>
> --8<------------------------------------------------------
> # Restrictions SMTP
> smtpd_helo_restrictions = reject_unknown_helo_hostname
> smtpd_sender_restrictions = reject_unknown_sender_domain,
> check_sender_access hash:/etc/postfix/sender_access
> smtpd_recipient_restrictions = permit_mynetworks,
> permit_sasl_authenticated,
> reject_rbl_client zen.spamhaus.org,
> reject_rhsbl_reverse_client dbl.spamhaus.org,
> reject_rhsbl_helo dbl.spamhaus.org,
> reject_rhsbl_sender dbl.spamhaus.org
> smtpd_relay_restrictions = permit_mynetworks,
> permit_sasl_authenticated,
> reject_unauth_destination
> smtpd_data_restrictions = reject_unauth_pipelining
> --8<------------------------------------------------------
>
> Most folks are using Thunderbird on Linux, and everything works
> perfectly. One single user has a MacBook Air with Thunderbird on Mac OS
> Mojave, and her outgoing mails are rejected with the following error
> message in /var/log/maillog on the server:
>
> --8<------------------------------------------------------
> Sep 16 14:22:32 sd-48011 postfix/smtps/smtpd[14434]: NOQUEUE: reject:
> RCPT from villa.figaret.pck.nerim.net[62.212.106.47]: 450 4.7.1
> <Air-de-bea.scholae.lan>: Helo command rejected: Host not found;
> from=<xxxxx.yyyyyyyy@xxxxxxxxxx> to=<info@xxxxxxxxxxxxx> proto=ESMTP
> helo=<Air-de-bea.scholae.lan>
> --8<------------------------------------------------------
>
> As far as I understand, it has to do with this MacBook's host
> configuration.
http://www.postfix.org/postconf.5.html#reject_unknown_helo_hostname
reject_unknown_helo_hostname (with Postfix < 2.3: reject_unknown_hostname)
Reject the request when the HELO or EHLO hostname has no DNS A or MX record.
The reply is specified with the unknown_hostname_reject_code parameter (default: 450) or unknown_helo_hostname_tempfail_action (default: defer_if_permit). See the respective parameter descriptions for details.
Note: specify "smtpd_helo_required = yes" to fully enforce this restriction (without "smtpd_helo_required = yes", a client can simply skip reject_unknown_helo_hostname by not sending HELO or EHLO).
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