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Poco Forums • View topic - verifying sender addresses

verifying sender addresses

General email topics, from anti-virus and anti-spam software to webmail and ISPs

Moderators: Eric, Tomas, robin

verifying sender addresses

Postby ghardenb » Sat Apr 22, 2006 6:05 am

Is there a method or an app out there that will automatically test the authenticity of the "from" address on each incoming email? Similar to what Spamcop does when we submit spam?
ghardenb
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Postby Michael » Sat Apr 22, 2006 6:26 am

I don't know of one but the best any utility could do would be to check that the syntax of the email address is correct and, possibly, that the domain actually exists. To the best of my knowledge there is no way to verify that a syntactically correct email address at a valid domain is authentic.
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Postby robin » Sat Apr 22, 2006 7:10 am

You can do it - but I suspect not easily with PocoMail.

The "conversation" for sending mail is actually quite simple. The sending computer makes a connection with the receiving server; one of the things that it says is "I have mail for xxx@domain". the receiving server either says "OK, I know that" or "Nope, don't know that". The action you take depends upon the response.

This conversation does not include the "To:" address in the message itself which is quite separate [this is how "BCC:" messages are sent].

You would also have to go through the process of finding out the IP address of the receiving machine from the bit after the "@": again not difficult.

The other thing to bear in mind is that when you try and connect, you may find that the address that you are trying to connect from is "blacklisted" because it is simply an IP address allocated by your ISP - which shouldn't be trying to send messages (in other words it could be a compromised PC being used by a spam trojan).

When you send messages from your PC, you usually send it via an SMTP relay provided by your ISP - this computer is recognised as a valid computer for transferring messages.

So, nice idea and can be done in theory. In practice there are a lot of hurdles; some insurmountable.

As a side issue, if you try and send a message to someone like IANA, you get a reply from an automated system. All messages are quarantined. You have to reply to the automated reply, or click on a web link, for your message to be delievered. It is quite clear from this that spam messages cannot be delivered because they will never receive the automated reply!
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