Key takeaway: Gateway DLP only inspects email at send time. MSG, PST, EML, and OST archives — stored on file shares, desktops, and cloud storage — contain years of PII, PHI, and financial data that most DSPM tools never scan. Email archive scanning is a required component of any complete data security posture management strategy.
If you walk into most security teams today and ask how they “protect email,” you’ll hear a familiar story: secure gateway, phishing filters, transport DLP, maybe some sandboxing. All of that matters. But it’s solving the wrong half of the problem.
The real risk is not email in transit. It’s email at rest.
The Email Data Security Gap: What Lives in PST, MSG, and EML Archives
Every organization I’ve worked with has the same pattern: MSG files saved to desktops, PST archives dumped onto file shares, EML files zipped and uploaded to cloud storage. Those archives contain years of attachments, forwarded threads, and exported mailboxes. They also contain some of the densest concentrations of PII, PHI, financial data, and confidential conversations anywhere in the company — and for most data security tools, they’re completely invisible.
Gateway DLP inspects a message once, at send time. It has no idea what happens when that message is saved, exported, forwarded, archived, or bundled into a PST file on someone’s last day at the company. If your data security posture management (DSPM) strategy doesn’t include deep, format‑aware email archive scanning, you’re blind to where email data actually lives.
How Sentra Scans Email Archives: MSG, EML, PST, and OST
At Sentra, we treat MSG, EML, PST, and OST as composite data stores that deserve the same depth of analysis as a database or a data lake table. Our extraction engine understands Outlook message files, standard RFC 822 emails, and full mailbox data files. We pull out headers, HTML and plain‑text bodies, and every attachment, then recursively follow the chain as far as it goes — attached emails, nested ZIPs, the spreadsheets and PDFs hiding inside those ZIPs, and so on. All of that processing happens in memory, so we’re not creating new, unmanaged copies of sensitive content while we scan.
Three Risks That Email Archive Scanning Directly Addresses
From a risk perspective, this matters in three concrete ways. First, insider exfiltration doesn’t always look like a big transfer to an external file‑sharing service. More often, it looks like months of forwarding sensitive files to a personal account, followed by a mailbox export to PST. That one file now contains everything they walked out with, in a format most tools can’t inspect. Second, accidental exposure is endemic: people send spreadsheets with customer PII, lab results, or financial reports to the wrong recipients all the time. Those messages live in archives long after anyone remembers they exist. Third, every major privacy and sectoral framework — GDPR, HIPAA, SEC/FINRA rules — assumes you can actually find personal and regulated data in email when you need to respond to a deletion request, an investigation, or legal discovery.
Email archives are one of the largest ungoverned data lakes in most enterprises. Treating them as “solved” because you have a good gateway is how you end up explaining to regulators why a PST on a public share contained ten years of customer attachments. Deep email archive scanning is exactly the kind of capability we built Sentra’s DSPM platform to deliver. If you’re serious about closing real‑world data gaps, you have to go where the data actually lives — and a staggering amount of it still lives in email.
Learn more about how Sentra discovers and classifies sensitive data across your cloud — including inside email archives — at sentra.io.
