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The VRFY command in ESMTP servers is an easy way for spammers to collect email adresses. Connecting to an ESMTP server and issuing a VRFY command with an email address will return a result of either 250 (address exists) or 557 (address does not exist). By sending multiple VRFY requests with arbitrary strings it is possible to generate a list of email addresses that are valid on the server, to be used for spam or as a basis for brute-force password attacks later. NTMail has an option to disable the VRFY command, but it does not in fact do anything. even if set to 'disable' the server will still processs and respond to VRFY requests.

The VRFY command in ESMTP servers is an easy way for spammers to collect email adresses. Connecting to an ESMTP server and issuing a VRFY command with an email address will return a result of either 250 (address exists) or 557 (address does not exist). By sending multiple VRFY requests with arbitrary strings it is possible to generate a list of email addresses that are valid on the server, to be used for spam or as a basis for brute-force password attacks later. NTMail has an option to disable the VRFY command, but it does not in fact do anything. even if set to 'disable' the server will still processs and respond to VRFY requests.