From: Alex Schuilenburg (alexsecoscentric.com)
Date: Fri Dec 02 2005 - 11:29:02 CST

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I have recently turned on reject_unverified_recipient for our backup MX
host which simply acts as a relay. This was done in an attempt to cut
down on the spam that gets queued there to non-existant local addresses.

Unfortunately I have since found out that the 450 message any sender
includes the internal VPN addresses and host names of the verification
host. The message they see is:

450 <fooecoscentric.com>: Recipient address rejected: unverified
address: host <internal name>[<internal addr>] said: 450
<fooecoscentric.com>: Recipient address rejected: User unknown in local
recipient table (in reply to RCPT TO command)

with <internal name> and <internal addr> being names and addresses of
hosts on our VPN.

Is there any configuration option of postfix to hide these names and
addresses for verification hosts?

I know can get round this by setting the relayhost to be the externally
visible i/f of the mail host (and primary MX) - and have it currently
configured like this. This will only show the visible interface.
However, the mail host eventually will reside only on the vpn behind a
firewall so these addresses and names ideally need to be hidden from the
user.

Thanks
-- Alex

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