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I am generating email from an .ASP page using JMail:


Kerio Mail Server says:

<- 421 4.4.5 Directory harvest attack detected
localhost failed with the message: "421 4.4.5 Directory harvest attack detected"

I can't find anything in the Help files that will tell me how to prevent this logjam. How does the mailserver detect this attack, and what can I do to prevent this false detection?

Ron Wodaski

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Could it be that you have the default Spam Greeting delay enabled ? Try to lower the value from 25 to 10.

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In Kerio, click on the SMTP SERVER link on the left side, and then the SECURITY OPTIONS tab. Look at the "Max number of unknown recipients (directory harvest attack protection):" setting. This means that after {Setting#} number of bad email addresses that the server has received, the email is considered to be an attempt to find good email addresses by sorting out the returned bad-address notices received from your Kerio server.

Check that you don't have that number set to low. Also check what email addresses you are sending to, that they are valid ones.
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