Philter Desktop redacts email files that end in .eml (the standard email format used by most mail
programs) and .msg (the format Microsoft Outlook uses when you save or drag out a message).
What gets redacted
When Philter Desktop redacts an email, it cleans up the subject line, the From / To / Cc
addresses, and the message body, according to your policy, the same way it handles any other
document. This covers the plain-text and HTML versions of the body; an Outlook message whose body is
only rich text (RTF) is recovered as text and redacted too, rather than being dropped. If the email
forwards or embeds another message (a message/rfc822 part), that nested message is redacted the
same way — its own Subject, From / To / Cc, and body are cleaned, and (when the header options below
are on) its technical and identity headers are stripped too. It also (by default) strips the technical headers that
would otherwise reveal the sender's IP, mail program, and the server delivery trail, and the common
identity headers (Bcc for blind-copy recipients, Reply-To, Sender, and Resent-…) that
aren't part of the visible From / To / Cc fields and so wouldn't otherwise be redacted. Both are on by
default and can be turned off in Settings → Email. If you turn off the identity-
header option, those headers (including Bcc) are kept as-is and not redacted, so their addresses
will remain in the output — review them before sharing.
You can also choose to remove the Date header (the email's send time). This is off by default — the send date is usually wanted and isn't personally identifying on its own — but if you need to remove it, turn it on in Settings → Email. When on, the Date header is dropped outright, so the send time is removed no matter how it is formatted (this does not rely on the policy recognizing a date). A timestamp can still appear inside the delivery trail; leave the technical-header option on to strip that too.
Attachments and images are not redacted
Philter Desktop redacts the email message itself: the subject, the addresses, and the body text.
It does not open, inspect, or redact attachments (a PDF, Word file, spreadsheet, image, or
anything else carried along with the email), and it does not read text inside images —
including inline images embedded in the body, such as a logo, a scanned signature, or a pasted
screenshot. By default both are copied through unchanged, so sensitive information inside an
attachment, or shown only inside an image, is left exactly as it was. If an email has attachments
that need redacting, save each one out as its own file and redact it separately (a .pdf,
.docx, or .txt attachment can go straight through Philter Desktop). Always review the finished
email and its attachments before sharing it.
If you would rather the redacted email carry no attachments at all, turn on Remove attachments
from redacted email in Settings → Email. When on, attachments are
deleted entirely — not redacted: their content is never inspected, and the attached files (and
their filenames, which can themselves reveal information such as john_smith_ssn.pdf) are removed
from the output. This option is off by default. Underneath it, Also remove inline images
(available only when the option above is on) does the same for the pictures embedded in the body:
they are deleted and their cid: references are neutralized. Leave it off to keep images such as a
corporate logo.
Whenever a redacted email still carries attachments or inline images, verification adds a warning reminding you that their content wasn't inspected — so review the original before sharing.
Outlook .msg files become .eml
Outlook .msg files are saved in a different format after redaction: a redacted .msg is saved as
an .eml file. Redacting message.msg therefore produces message_redacted-draft.eml, not a .msg.
The format changes because .msg is Microsoft's own private, undocumented Outlook format. Philter
Desktop can reliably read a .msg and extract everything it needs to redact, but it cannot
guarantee that a rebuilt .msg file would faithfully preserve every part of the message. Rather than
produce a .msg that might be subtly corrupted, it writes the redacted result as .eml, the
universal email format. An .eml file is a complete, standalone copy of the email that opens in
Outlook (double-click it) as well as in Apple Mail, Thunderbird, Gmail's import, and essentially
every other mail program. Nothing is lost in the redaction itself; only the container file type
changes.
.eml files redact to .eml, and everything else keeps its original file type as usual; only .msg
changes.
For adding files to the queue, previewing, adjusting, verifying, and reporting on a redaction, see Redacting Documents.