Email is one of the top attack vectors for getting inside an organization, and it is a known fact that we are more likely to open an email that purports to come from someone we know.
The spammers of course know this too, and recently, they have been exploiting it by intentionally creating a kind of “nested” email address.
How this accomplished is a little technical (and you can read about it here), but it’s increasingly being used to spoof the “From:” portion of an email.
The good news in Zimbra (or any Linux server running the Postfix MTA) is that it’s easy to fix.
One of Zimbra’s Super Star engineers, Rick King, recently published a How-To specifically for implementing this fix within Zimbra. If you are responsible for the security of your company’s Zimbra system, you can find Rick’s tutorial here.
Note that when you do a Zimbra version upgrade (not a Patch), you’ll need to redo Rick’s edit to the /opt/zimbra/conf/zmconfigd/smtpd_sender_restrictions.cf file.
L. Mark Stone
Mission Critical Email
4 December 2018
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