EML Viewer, Email Headers & MBOX Viewer

Name: EML Viewer, Email Headers & MBOX Viewer
Author: Zovo

EML Viewer, Email Headers & MBOX Viewer, a VS Code extension by Zovo

EML viewer and email viewer for .eml, .emlx and .mbox files in VS Code. See the HTML with remote images blocked, attachments, SPF/DKIM/DMARC results and the delivery route. Offline.

Install in VS Code Open the Marketplace page

Free, MIT license. Needs VS Code 1.90.0 or newer. Extension ID zovo.eml-viewer, version 0.1.5.

Read saved .eml, .emlx and .mbox email files in VS Code the way a mail client shows them, with remote images blocked until you ask for them.

Real output from VS Code 1.142 on macOS. The file is newsletter.eml, made by scripts/make-samples.js with made-up people at example.com. scripts/e2e-vscode.mjs installed the packaged extension in a clean VS Code profile, opened the file and saved the window through the debug port.

Opening a message doesn't tell the sender. Tracking pixels and other remote images stay blocked, and the bar says how many there are. One click shows them for that tab. Inline cid: images and attachments come from the file itself, so they always show.
You can check where a message came from. The badges show the SPF, DKIM and DMARC results that the receiving server recorded, and the Route tab lists every Received hop with the delay between hops.
Whole mailboxes open fast. A .mbox file is indexed as a stream, so the first 200 messages show while the rest is still being read. A 42 MB mailbox with 39,000 messages was fully indexed in 0.3 s in our test.
Scripts in a message never run. The HTML body sits in a sandboxed frame without script rights, and scripts, frames, forms, meta refresh and javascript: links are removed first.

Quick start

Install EML Viewer.
Click any .eml, .emlx, .mbox or .mbx file in the Explorer.

If another editor opens, right-click the file and pick "Open in EML Viewer", or use "Reopen Editor With..." from the editor title menu. That also works for mailboxes with no extension, such as Thunderbird's Inbox file. "EML Viewer: Get Started" in the Command Palette opens a short tour.

Questions people ask

Is EML Viewer, Email Headers & MBOX Viewer free?

Yes. EML Viewer, Email Headers & MBOX Viewer is free and MIT licensed.

How do I install EML Viewer, Email Headers & MBOX Viewer?

Click "Install in VS Code" above, or search for zovo.eml-viewer in the Extensions view.

What you see for each message

Part	What it shows
Header card	Subject, From, To, Cc, Bcc, Reply-To (when it differs from From) and the date in your time zone
Badges	SPF, DKIM and DMARC results, green for pass, red for fail, yellow for none or neutral
Attachments	Name, size and a Save button. Names are cleaned, so a name can't point outside the folder you pick
Message	The HTML body in a sandboxed frame. Links ask before they open in your browser
Text	The plain text part, or text made from the HTML when there is none
Authentication	Each Authentication-Results header, every DKIM signature (domain, selector, algorithm), Received-SPF and the ARC chain
Route	Received hops, oldest first, with hostnames, IPs, protocol, TLS and the delay between hops. Hops over 5 minutes are marked
Headers	Every header line, with Copy
Source	The raw message (the first 2 MB), with Copy

The Authentication tab for a spoofed invoice. Three cards read SPF FAIL, DKIM NONE and DMARC FAIL. Below them the Authentication-Results header from mx1.example.org lists spf=fail for , dkim=none and dmarc=fail with p=QUARANTINE, and the Received-SPF line is shown in full.

The results are the ones the receiving server wrote. EML Viewer doesn't query DNS or check signatures again, which keeps it offline. A message from a Sent folder or written by a script often has no Authentication-Results header, and the tab says so.

The Route tab for the same message. Two hops, oldest first. Hop 1 goes from unknown-host.example.net at 192.0.2.77 to mx1.example.org over SMTP. Hop 2 goes from mx1.example.org to mailstore.example.org over LMTP and is marked +9 min 0 s in yellow.

Mailboxes

team-inbox.mbox with 2,500 messages. The left pane has a search box, a sort menu set to Newest first and a list of senders, subjects, dates and sizes, with a paperclip on messages that have attachments. The selected message is open on the right in the same view as a single .eml file.

Search matches sender, recipients and subject. Every word you type has to match.
Sort by file order, newest or oldest first, sender, subject or size.
The list shows 200 messages per page. Arrow keys, or J and K, move to the next and previous message.
Each message is read from disk when you pick it, so a big mailbox doesn't fill memory.
Both mboxo and mboxrd files work. A From line only starts a new message at the top of the file or after a blank line, and >From quoting is undone.

Files and limits

File	Notes
`.eml`	One RFC 822 message, as saved by Outlook, Thunderbird, Gmail and most other clients
`.emlx`	Apple Mail's format. The byte count line and the trailing property list are skipped
`.mbox`, `.mbx`	Mailboxes from Thunderbird, Gmail Takeout, Apple Mail export and mail servers

Files over 4 GB show a message instead of opening. A single message over 200 MB (setting emlViewer.maxMessageMB) also shows a message, and "Open as text" in the toolbar opens the raw file either way. Outlook .msg and .pst files are not supported.

Settings

Setting	Default	What it does
`emlViewer.alwaysShowRemoteImages`	false	Load remote images in HTML messages without asking.
`emlViewer.maxMessageMB`	200	Largest single message that is parsed, in MB.
`emlViewer.askForRating`	true	Ask one time for a Marketplace rating after a few days of use. Nothing is sent anywhere.
`emlViewer.showSupportLinks`	true	Show the small Sponsor and More free viewers links in the status line.

Privacy and safety

EML Viewer makes no network calls and has no telemetry. The only requests it can cause are the remote images you choose to show and the links you confirm. The mail file is never written. The only files the extension writes are the attachments you save, and it refuses to save over the mail file itself.

The webview runs under a strict Content Security Policy. Its scripts need a per-load nonce, and the message frame has no script rights at all. Subjects, names and header values are shown as plain text, so a subject such as `` stays text.

The unsafe HTML test message. Its subject is shown as literal text. In the body the script, iframe, object, meta refresh, base tag and javascript link are gone, the remote pixel and CSS background are blocked, and the form has no action.

License

MIT. Messages are parsed with postal-mime (MIT-0). See THIRD-PARTY-NOTICES.md.

Install EML Viewer, Email Headers & MBOX Viewer

Click the button to open VS Code and install it, or press Ctrl+P (Cmd+P on macOS) in VS Code and run ext install zovo.eml-viewer.

Install in VS Code Open the Marketplace page

Free, MIT license. Needs VS Code 1.90.0 or newer. Extension ID zovo.eml-viewer, version 0.1.5.

Source code and issues are on GitHub.

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Support this work

If this extension saves you time, you can support the work on GitHub Sponsors. Monthly tiers start at $5, and one-time tiers start at $15. Sponsorship is optional, and the tool works the same without it.

Zovo on GitHub