Re: Tool for validating sender address as spam-fighting technique?

[John Rudd]

Matt Hampton wrote:
Wolfgang
what happens if I put one such thing on my mailserver too and want to 
send you a mail?
My outgoing MX starts a smtp connection, and then, at RCPT TO, your 
system
starts a smtp dialogue with my incoming MX. Unless the machines are 
tightly coupled,
my incoming MX does not expect to get a verification probe - it will 
believe that you try
to send me some mail, and probe your machine.
This looks like a source of infinite loops :(

All of the milters are configured with an address verfication address. 
This is used as the sender when verifying addresses and so when the 
address is seen in an incoming session it is allowed through.

I use [EMAIL PROTECTED]


The correct answer is:

When trying to validate a sender, and you do a call-back probe (as this 
technique is already in use by places like verizon, and has been for 
years), you should use <> as your sender address.  The other side knows 
it's valid immediately (because RFCs say so), and thus the other side 
doesn't need to try to do a call-back on you, creating potential for an 
infinite loop.