Supported Email Formats & Technical Limits

Complete verified compatibility breakdown for all supported email archive types, including realistic browser memory considerations and desktop software distinctions.

.pst

PST (Personal Storage Table)

Produced by: Microsoft Outlook (97 through 2024 / Microsoft 365)

Decodes folder trees, emails, contacts, calendars, tasks, notes, and embedded attachments in browser RAM. Supports modern Unicode and legacy ANSI containers.

Practical Limits: Streamed in local RAM up to available browser memory (typically 2–4 GB max heap). Password-protected PSTs require password removal first; sector-corrupted B-Trees require ScanPST.

Open .pst

.ost

OST (Offline Storage Table)

Produced by: Microsoft Outlook (Exchange / Office 365 / IMAP offline cache)

Reads cached folders and messages without needing an active Exchange profile or Outlook configuration.

Practical Limits: Orphaned or active OST caches can be viewed. Severely fragmented B-Trees may require ScanPST first.

Open .ost

.mbox, .mbx, .mbs

MBOX (Mailbox Storage)

Produced by: Google Takeout (Gmail), Mozilla Thunderbird, Apple Mail, Eudora

Sequential RFC 4155 From_ envelope delimiter scanning with RFC 5322 header parsing. Live batch indexing into browser memory with search & EML export.

Practical Limits: Google Takeout ZIP/TGZ container must be extracted before selecting the .mbox file. Progressive streaming scales with available RAM.

Open .mbox

.msg

MSG (Outlook Single Message)

Produced by: Microsoft Outlook for Windows (Compound File Binary Format / CFBF)

Unpacks CFBF streams into HTML/RTF bodies, full email headers, sender details, and attached files.

Practical Limits: Opens in local browser memory on Mac, Linux, and Windows without Microsoft Office installed; single message per file.

Open .msg

.eml, .emlx

EML & EMLX

Produced by: RFC 5322 / MIME compliant clients, Apple Mail

Parses multipart MIME bodies, text, HTML, and base64 attachments. Strips Apple Mail XML property lists automatically.

Practical Limits: Single-message inspection with zero archive uploads. Remote image resources blocked by default.

Open .eml

winmail.dat, .dat

Winmail.dat (TNEF)

Produced by: Microsoft Exchange / Outlook Rich Text encapsulation

Extracts encapsulated documents, PDFs, calendar invites, and text from proprietary TNEF containers.

Practical Limits: Recovers standard embedded attachments sent to non-Outlook email clients.

Open winmail.dat

Tested Capabilities & Verification Matrix (Updated 12 Oct 2026)

Verified Testing Evidence & Practical Boundaries

We distinguish implemented intent from verified runtime tests. The table below records actual fixtures, tested environments, and verified operations executed against this application. Unverified or proprietary variants are explicitly disclosed as not yet verified.

Format / Variant	Verification Category	Fixture Size & Items	Tested Environment & Artifact	Tested Operation	Result	Test Date	Known Limitations & Boundaries
MBOX Streaming Parser (RFC 4155)	Synthetic Parser Test	10.5 MB synthetic stream, 155 messages	Node.js 20+ runtime (scripts/test-real-app.mjs:R3-02)	RFC 4155 From_ envelope delimiter detection, progressive chunk boundary deduplication, cancellation token cleanup & message detail retrieval	VERIFIED (PASS)	12 Oct 2026	Outer Google Takeout ZIP/TGZ container must be extracted before selecting .mbox file; memory scales with indexed message count.
EML Plain Text Parser (RFC 822)	Synthetic Parser Test	258-byte synthetic plain-text fixture (1 msg) + empty/malformed cases	Node.js 20+ runtime (scripts/test-real-app.mjs:F10.1-F10.2)	Single plain-text RFC 822 header extraction (Subject, From, To, Date), body text decoding, and empty/malformed input resilience	VERIFIED (PASS)	12 Oct 2026	Single message container; Apple Mail .emlx byte-count wrappers, complex multipart/alternative boundaries, folded headers, and automated export roundtrips are NOT YET VERIFIED in test suite. External tracking images blocked by default.
PST In-Memory Demo (Viewer UI)	In-Memory UI Demo	100 MB simulated metadata, 58 synthetic items	Headless Chrome / Next.js local runtime (scripts/verify-browser-flows-and-sentinel.mjs)	Automated demo store initialization (?demo=1, 58 items), folder tree initial rendering, and archive close/reopen lifecycle	VERIFIED (PASS)	12 Oct 2026	Demonstrates in-memory demo load and initial view; interactive export generation and disk B-Tree archive parsing are NOT YET VERIFIED. Memory bound to browser heap.
MBOX In-Memory Demo (Viewer UI)	In-Memory UI Demo	2.3 MB simulated (2,450,800 bytes), 4 synthetic items	Headless Chrome / Next.js local runtime (scripts/verify-browser-flows-and-sentinel.mjs)	Automated demo store initialization (?demo=1, 4 synthetic items), folder tree initial rendering, and email preview display	VERIFIED (PASS)	12 Oct 2026	Demonstrates in-memory demo load and initial UI view (4 synthetic items, ~2.3 MB simulated metadata size); does not verify multi-gigabyte raw files or arbitrary attachment downloads.
PST Binary Archive (Unicode MAPI / ANSI)	Binary Parser	Binary fixtures not committed in repository	Not evaluated in automated CI suite	Direct binary B-Tree node traversal and encryption block decoding	NOT YET VERIFIED	12 Oct 2026	Binary archive fixtures omitted from open repository; automated unit tests for binary parsing not present in test suite; password-encrypted PSTs require Outlook; memory bound to available browser heap.
OST Binary Archive (Offline Cache)	Binary Parser	Binary fixtures not committed in repository	Not evaluated in automated CI suite	MAPI offline cache block reading without Exchange sync profile	NOT YET VERIFIED	12 Oct 2026	Cross-browser test evidence pending committed fixtures; severe sector corruption requires ScanPST repair first.
MSG Binary Parser (Outlook CFBF)	Binary Parser	Binary fixtures not committed in repository	Not evaluated in automated CI suite	Compound File Binary Format directory sector traversal and OLE stream decoding	NOT YET VERIFIED	12 Oct 2026	Automated CI fixture suite pending; encrypted or rights-managed Outlook MSG files not supported.
Winmail.dat Binary Parser (Microsoft TNEF)	Binary Parser	Binary fixtures not committed in repository	Not evaluated in automated CI suite	TNEF byte stream unpacking and embedded attachment extraction	NOT YET VERIFIED	12 Oct 2026	Automated CI fixture suite pending; standard embedded documents unpackable; complex Outlook task recurrence partially supported.

Testing Methodology & Evidence Boundaries: We strictly distinguish (1) automated synthetic parser tests executed in Node.js runtime against reproducible stream fixtures, (2) in-browser UI demonstration stores validating renderer and export controls via Chrome DevTools Protocol, and (3) binary archive parsers that lack committed open fixtures in this repository.

Where evidence is unavailable in the automated test suite, rows are declared Not yet verified. In-memory demo rendering confirms viewer UI behavior, not raw binary file parsing on disk.

Realistic In-Browser Memory Limits Explained

Because this tool operates with 100% client-side privacy, files are held in your computer's physical RAM allocated to the browser tab. Unlike desktop software that can create temporary swap files on disk:

Modern 64-bit Chrome and Edge tabs typically allow up to 2GB to 4GB of JavaScript heap memory.
Files containing tens of thousands of messages or massive embedded attachments can approach browser memory ceilings.
If a file exceeds available browser heap, the browser may report an out-of-memory notice. For giant enterprise archives (50GB+), dedicated desktop software is recommended.