Threat hunting using DNS indicators

DNS is a great source of information for security analysts… if you’re not already monitoring DNS activity in your network — you should start asap, for the reasons we’ll explore in this article DNS is one of the major workhorses that powers the Internet. Everything uses DNS — browsers, apps, updates… and malware. Almost every malware needs to “phone … Continue reading Threat hunting using DNS indicators

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Email Error: 450 Client host rejected

A couple of our clients sometimes have issues when sending email, with a returned non-delivery report stating the following: Peer server rejected email: 450 Client host rejected: 'cannot find your hostname' It turns out this is a very strict check (usually performed by postfix), that is controlled via the directive reject_unknown_client_hostname in the postfix configuration. The documentation … Continue reading Email Error: 450 Client host rejected