On Monday 24 January 2005 16:01, [EMAIL PROTECTED] wrote:

> I am sending a mail from the user [EMAIL PROTECTED]
> Local host is amalasingh.com is configured and works fine from inside and
> outside.
<snipped>
> ******************
> Jan 24 20:50:37 localhost postfix/qmgr[3875]: B21F078061:
> from=<[EMAIL PROTECTED]>, size=659, nrcpt=1 (queue active) Jan 24 20:51:09
> localhost postfix/smtp[5460]: B21F078061: host
> leeds.sin1.netline.net.uk[213.40.2.10] said: 451 Could not complete sender
> verify callout (in reply to RCPT TO command)

The receiving server is telling you that it is unable to verify your email 
address as being a valid email address.

Make sure this feature is working on your Mail server (via instructions 
below)or contact the admin of the mail server and ask him to whitelist you.

From Spam Filtering HowTo on Ibiblio.org

2.3.2.4. Sender Callout Verification

This is a mechanism that is offered by some MTAs, such as Exim and Postfix, to 
validate the "local part" of a remote sender address. In Postfix terminology, 
it is called "Sender Address Verification". 

Your server contacts the MX for the domain provided in the sender address, 
attempting to initiate a secondary SMTP transaction as if delivering mail to 
this address. It does not actually send any mail; rather, once the RCPT TO: 
command has been either accepted or rejected by the remote host, your server 
sends QUIT. 

By default, Exim uses an empty envelope sender address for such callout 
verifications. The goal is to determine if a Delivery Status Notification 
would be accepted if returned to the sender. 

Postfix, on the other hand, defaults to the sender address <[EMAIL PROTECTED]> 
for address verification purposes (domain is taken from the $myorigin 
variable). For this reason, you may wish to treat this sender address the 
same way that you treat the NULL envelope sender (for instance, avoid SMTP 
transaction delays or Greylisting, but require Envelope Sender Signatures in 
recipient addresses). More on this in the implementation appendices. 

You may find that this check alone may not be suitable as a trigger to reject 
incoming mail. Occasionally, legitimate mail, such as a recurring billing 
statement, is sent out from automated services with an invalid return 
address. Also, an unfortunate side effect of spam is that some users tend to 
mangle the return address in their outgoing mails (though this may affect the 
"From:" header in the message itself more often than the Envelope Sender). 

Moreover, this check only verifies that an address is valid, not that it was 
authentic as the sender of this particular message (but see also Envelope 
Sender Signature). 

Finally, there are reports of sites, such as "aol.com", that will 
unconditionally blacklist any system from which they discover sender callout 
requests. These sites may be frequent victims of Joe Jobs, and as a result, 
receive storms of sender callout requests. By taking part in these DDoS 
(Distributed Denial-of-Servcie) attacks, you are effectively turning yourself 
into a pawn in the hands of the spammer.

-- 
Bryan Phinney


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