Fighting malware and spam

Directory harvesting

Building a list of email addresses by trying many combinations

Directory harvesting is a technique used by spammers to gather lists of functioning email addresses on a given server. By sending a stream of test mails to the server running through a large number of possible addresses, the bounced and successful messages can be analysed to provide a list of addresses which are accepted by the server.

This is one explanation for the occasional blank spam message.