How to Convert an OST Mailbox to JSON

For IT and compliance teams, an orphaned OST is data that needs reviewing: what was sent, to whom, when. JSON lets you load the whole mailbox into a script or database and query it, instead of clicking through emails one at a time.

What the output looks like

One array, one object per email:

{
  "folder": "Sent Items",
  "subject": "Contract signed",
  "from": [{ "name": "Ana Silva", "address": "ana.silva@company.com" }],
  "to": [{ "name": "Legal", "address": "legal@company.com" }],
  "cc": [],
  "date": "2022-11-04T15:30:00.000Z",
  "text": "Please find the signed contract attached.",
  "html": "<p>Please find the signed contract attached.</p>",
  "attachments": [{ "name": "contract.pdf", "type": "application/pdf", "size": 241337 }]
}

text is always present, generated from the HTML if needed. html is null for plain-text emails.

How to convert OST to JSON with ZapMorph

1. Open the converter

Go to the OST to JSON converter.

2. Add the OST

Drop in the .ost file. Close Outlook first if it's running on the same machine.

3. Convert and download

Click Convert to JSON.

Example queries

Emails to external domains (Python):

import json
mail = json.load(open("mailbox.json", encoding="utf-8"))
external = [m for m in mail if any(not r["address"].endswith("@company.com") for r in m["to"])]
print(len(external), "emails sent outside the company")

Emails per month (JavaScript):

const counts = {};
for (const m of mail) if (m.date) counts[m.date.slice(0, 7)] = (counts[m.date.slice(0, 7)] ?? 0) + 1;
console.table(counts);

Command line with jq: jq '[.[] | select(.attachments | length > 0)] | length' mailbox.json counts emails with attachments.

Why JSON over CSV?

Troubleshooting

"Isn't a readable Outlook data file." Damaged, or an OST in a newer Outlook 2013+ internal format that can't be read. If the account still exists, export from Outlook or webmail.

"Password-protected." The OST uses encryption that can't be read outside Outlook. If the account still exists, export from Outlook or webmail instead.

Related

• Prefer a spreadsheet? OST to CSV.
• Explore the JSON in the JSON viewer.
• Counts by folder, year and sender without code: PST Analyzer (reads OST too).

Summary

The OST to JSON converter turns an Outlook offline mailbox into structured data for review and analysis, privately in your browser.