Email file tools

An email file is correspondence. Not an extract of it — the whole message, with every recipient, the routing that carried it, the headers that say which machines touched it, and whatever was attached. It is frequently the thing somebody is keeping because it matters: a contract, a dispute, a record for an accountant, an exhibit.

The tools you find when you search for a way to open one all ask you to upload it. The best-known converter markets its output as a court-ready PDF, which describes the use case exactly and describes what is being sent to a stranger’s server rather less comfortably. The most-read guide to opening .eml files tells its reader not to put anything privileged through a random online tool — and then lists online tools, because at the time of writing there was nothing else to list.

The other half of the market does not ask you to upload anything. It asks you to install something: a Windows or Mac program, usually free to read and paid to export. That is a reasonable answer, and it is a strange amount of ceremony for reading one file somebody sent you.

These read the file in your browser. You can check that the way you can check anything here — open the Network tab and use a tool, or go offline after the page loads and use it anyway.

Opening an email can tell the sender you opened it. A tracking pixel is an ordinary image on somebody else’s server with a URL unique to you, and fetching it reports the open, the time, your address and your browser. It is why every serious mail client stopped loading remote images by default and started asking first.

An online viewer that renders the message renders that image too. The viewer here does not fetch remote content at all and says so on the page when it finds some, so reading a message costs the sender nothing and tells them nothing. How a remote image tells the sender you opened it is the longer version.

Somebody sent you a file and nothing opens it

A .eml is one message as plain text and the viewer reads it: sender, date, subject, body and what came attached. If the file is .msg it came out of Outlook and is a different thing entirely — a binary container rather than text — so convert it first and the rest of this section will read it. Which extension is which explains why there are four of them.

You only want what was attached

The attachment extractor lists what is in the message and decodes it out of the base64 it travelled in, without rendering the message at all. If you have wondered why a 4MB photo arrives as 5.4MB, that is the encoding.

You are not sure the message is genuine

The From line is the one part of an email anybody can write. The header analyser shows the Received chain in the order the hops actually happened, and the SPF, DKIM and DMARC results underneath it — the parts that were checked rather than claimed. What a header actually tells you walks through a real one.

You have your whole mailbox in one enormous file

That is .mbox, and it is what Google hands you when you ask for your mail back. The viewer opens it and lists every message; the CSV export turns it into a spreadsheet you can sort and count; splitting it gives you one file per message instead of one file for everything.

Here the argument for doing it locally is not only about privacy. A Takeout archive runs to several gigabytes, and uploading it to convert it is slow enough to be its own reason not to. What Takeout actually gives you covers what is in the file and what is missing from it.

You need the message as a document

EML to PDF puts the headers and the message on a page, for a filing or a record. It lays the text out rather than reproducing the sender’s HTML, which is a real limitation and is stated on the page rather than here. If you want the words and nothing else, EML to text drops the markup, the tracking pixels and the quoted-printable escapes.

For the spreadsheet end of a CSV export, the data section has the cleaner, the splitter and the converters. For what a PDF carries once you have made one, the PDF section has the metadata tools.