Anonymize an email (.msg, .eml) before giving it to an AI

What an email really contains

On screen, an email comes down to a few lines. The file carries much more.

Technical headers do not appear on screen, but they are in the .eml or .msg file: they trace the message’s path from server to server and reveal the mail domains on both sides. Attaching the raw file to an AI means handing all of that over.

The reply thread: where names hide

A reply to an email repeats the previous message below it, which repeats the one before, and so on. Each carries its own From, To, Sent and Subject lines, and often a full signature. In an exchange of ten messages, a person mentioned once in the first can reappear under three different spellings: “Mr. Martin”, “Jean”, “JM”.

Two habits: cut what the task does not need (to draft a reply, the last two messages are often enough), and review the rest line by line. Initials, first names alone and nicknames easily slip past automatic detection.

Attachments, to be handled separately

A .msg or .eml file contains the attachments themselves, not just a link. Sending the file means sending the attached contract, bank details or ID document. Save the useful attachments separately, anonymize them as documents (see anonymize a PDF, a Word document, an Excel file or a scan), and keep only those the task needs.

Saving an email as .msg or .eml

To handle an email like a document, you first need to save it as a file. Menus vary by version:

• Classic Outlook (Windows): double-click the message to open it, then File > Save As; choose a folder, a name and the file type (Outlook message, .msg).
• New Outlook (Windows): select the message, then More actions (the three dots) > Save as, or right-click the message > Save as.
• Outlook on the web: open the message, More actions > Download; the file lands in your Downloads folder.
• Apple Mail on a Mac: select the message, then File > Save As and choose the Raw Message Source format: you get an .eml file. Dragging the message to the desktop also gives an .eml file.

Keep these files in the matter folder, on the computer, not in an online shared space.

The manual method

For a short, single message, the manual method is enough:

1. Copy only the useful text into a plain-text editor (Notepad, TextEdit in plain-text mode): images, attachments and technical headers stay behind.
2. Delete the signature, the confidentiality notice and the quoted messages you do not need.
3. Replace each person, organization, address, phone number, email address and matter reference with a stable placeholder: [PERSONNE_1], [ORGANISATION_1]. Keep the mapping on the computer, in a separate file.
4. Review by searching for the original names, including first names, initials and nicknames.

The detailed method, with the instruction to give the AI, is in our guide to pseudonymize a document and put the real names back into the answer. It becomes tedious when you have to handle a whole exchange, or a file’s emails along with its documents.

The method with AnonymFiles

1. Drop in the folder, including .msg (Outlook) and .eml emails, with the attachments saved separately.
2. One text copy per email. The subject, sender, recipients (To, Cc, Bcc), date and message body are carried over into a Markdown copy; an HTML message is converted to text. Attachments are never copied: only their number is shown. Images and technical headers are not carried over.
3. Detection. Names, organizations, addresses, email addresses, French-format phone numbers, IBANs from nine European countries, private dates and ID numbers are replaced with stable placeholders, in the headers as in the body and the quoted thread. The same person keeps the same placeholder in the email, its replies and the other documents in the file.
4. Review. Each copy is shown next to the original; one click masks what detection missed (an initial, a nickname, a reference). Nothing is exported without approval.
5. Export and return. The copy goes to the AI; the mapping table stays on the computer. The app then puts the real names back into the AI’s answer.

Limits to know: each email is capped at 50 MiB, attachments included; an unreadable or nearly empty email is excluded and flagged. The app works with no account and no telemetry; the license is checked on the computer, with no network call. On a Mac, the detection models are included: no connection at all. On Windows, they are downloaded once, at the first processing run, without any document text (see the security page). Pricing: €290 excl. VAT per seat per year for one or two seats, €240 excl. VAT per seat from three seats, quote above twenty seats.