From: Stephen (sdw2shineonline.co.nz)
Date: Fri Aug 26 2005 - 01:05:23 CDT

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Hi All,

I've got an "interesting" little problem. We can't send mail to a
certain company - their mail server blocks mail from our mail server.
However, if I send mail directly from our proxy server, it is
delivered. (I've called the blocker, mailblocker.site below)

The gory details are listed below.

*Architecture*
Internal mail server is Postfix 2.0.6 (Redhat 8 - due for replacement)
Proxy server is Postfix 2.1.5 with Amavisd-new, razor, postgrey, and
spamassassin. The proxy server relays all mail into and out of our site.
mailblocker.site has the following header
         220 mailblocker.site ESMTP NetIQ MailMarshal (v5.5.6.7) Ready

*Observations*
I used netcat to send a message "manually" from the internal mail
server. The conversation is shown below:

[tagmsvr tag]$ nc 192.168.240.4 25
220 proxy.ourserver.co.nz ESMTP Postfix
ehlo ourserver.co.nz
250-proxy.ourserver.co.nz
250-PIPELINING
250-SIZE 10240000
250-ETRN
250 8BITMIME
mail from: tagourserver.co.nz
250 Ok
rcpt to: infomailblocker.site
data550 <infomailblocker.site>: Recipient address rejected:
undeliverable address: host mail.mailblocker.site[210.54.242.29]
said: 550 Rule imposed mailbox access for infomailblocker.site
refused (in reply to RCPT TO command)

I enabled logging of SMTP traffic on the proxy for the conversation
above. Observed that immediately after the "rcpt to" command is
entered, an SMTP connection is initiated from the internal mail
server to the proxy, and then from the proxy to mailblocker.site, and
mailblocker.site rejects this with a 550. The connection is rejected
even before I've had a chance to enter the DATA line in the SMTP
conversation.

Sending a message "manually" from the proxy server succeeds.

Please let me know any further information required. I didn't want to
make the post too long to start with.

I'd really appreciate a hand on this one. Its got me stumped

Thanks
Stephen

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