From: Matthias Schmidt (betaadmilon.net)
Date: Thu Sep 27 2007 - 08:24:30 CDT

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Am/On Thu, 27 Sep 2007 09:19:09 -0400 schrieb/wrote Dennis Putnam:

>I am getting complains from senders saying their mail is
>undeliverable. What is not clear is what server (the sender's or the
>receiver's) is generating the error. In any case I have no idea what
>it means. Can someone help? TIA.
>
>> The following message to <mymailboxmydomain.com> was
>> undeliverable. The reason for the problem: 5.1.0 - Unknown address
>> error
>> 500-'Firewall Error'
>
>I should note that this is intermittent as some mail gets through and
>it is only this sender's domain that has the problem. That implies to
>me that the problem is on the sender's server but I need more
>information.

they might have blocked the smtp port 25.
Ask the user to use the submission port 587 and configure postfix accordingly.
Here is how you change master.cf:

submission inet n - n - - smtpd
   -o smtpd_enforce_tls=no
   -o smtpd_sasl_auth_enable=yes
   -o smtpd_client_restrictions=permit_sasl_authenticated,reject

to enable the submission port.

Thanks and all the best

Matthias

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