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README.md

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+# Filter DKIMout
+
+[![Build Status](https://github.com/breard-r/opensmtpd-filter-dkimout/actions/workflows/ci.yml/badge.svg)](https://github.com/breard-r/opensmtpd-filter-dkimout/actions/workflows/ci.yml)
+![Minimum rustc version](https://img.shields.io/badge/rustc-1.64.0+-lightgray.svg)
+![License MIT OR Apache 2.0](https://img.shields.io/badge/license-MIT%20OR%20Apache--2.0-blue)
+
+DKIM filter for [OpenSMTPD](https://www.opensmtpd.org/).
+
+
+## Project status
+
+This is a work in progress, it is not supposed to work yet.
+
+
+## Frequently Asked Questions
+
+### Does this filter signs outgoing emails using DKIM or check the DKIM signature of incoming emails?
+
+It only signs outgoing emails.
+
+### Why create another filter for that?
+
+Currently, the options to sign outgoing emails with DKIM are the following:
+- [DKIMproxy](https://dkimproxy.sourceforge.net/usage.html)
+- [filter-dkimsign](https://imperialat.at/dev/filter-dkimsign/)
+- [filter-rspamd](https://github.com/poolpOrg/filter-rspamd)
+
+DKIMproxy is not an OpenSMTPD filter and is therefore more inconvenient to use. Moreover, its development stopped in 2013 and it is therefore dangerous to use.
+
+The two other are fine, however I think they lack a few features, like automatic key rotation and publication of obsolete private keys.
+
+### Why would anyone publish private keys, even obsolete ones? Are you crazy?
+
+DKIM's goal is to fight spam, that's all, and for that it only need the keys to be safe when the recipients receives the email. But because it includes a cryptographic proof over the content it is being used for other usages, mostly as a legal proof long after the email has been sent and received. Publishing the obsolete/revoked private keys allows the sender to regain deniability.
+
+Matthew Green wrote an excellent article on this subject: [Ok Google: please publish your DKIM secret keys](https://blog.cryptographyengineering.com/2020/11/16/ok-google-please-publish-your-dkim-secret-keys/).
+
+### Where is the documentation?
+
+A man page will be available by the time this filter is ready to use.