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.\" Copyright (c) 2019 Martijn van Duren <martijn@openbsd.org>
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.Dd $Mdocdate$
.Dt FILTER-DKIM 8
.Os
.Sh NAME
.Nm filter-dkim
.Nd add dkim signature to messages
.Sh SYNOPSIS
.Nm
.Op Fl a Ar algorithm
.Op Fl c Ar canonicalization
.Op Fl h Ar headers
.Op Fl t
.Op Fl x Ar seconds
.Op Fl z
.Op Fl Z
.Fl d Ar domain
.Fl k Ar file
.Fl s Ar selector
.Sh DESCRIPTION
.Nm
adds a dkim signature to the message.
The following flags are supported:
.Bl -tag -width Ds
.It Fl a
The algorithm to use.
This implementation only supports rsa cryptography.
Only sha256 should be used for hashing, since other algorithms are most likely
not supported by verifiers.
Defaults to
.Ar rsa-sha256 .
.It Fl c
The canonicalization algorithm used to sign the messge.
Defaults to
.Ar simple/simple .
.It Fl d
The domain where the public key can be found.
.It Fl h
The email headers which are included in the mail signature.
Per RFC this option requires at least the from header to be included.
The headers are specified by separating them with a colon.
The default is
from:reply-to:subject:date:to:cc:resent-date:resent-from:resent-to:resent-cc:in-reply-to:references:list-id:list-help:list-unsubscribe:list-subscribe:list-post:list-owner:list-archive .
.It Fl k
.Ar file
should point to a file containing the RSA private key to sign the messages.
.It Fl s
The selector within the _domainkey subdomain of
.Ar domain
where the public key can be found.
.It Fl t
Add the time of signing to the dkim header.
.It Fl x
Add the amount of
.Ar seconds
the signature is valid to the dkim header.
.It Fl z
Add the mail headers used in the dkim signature to the dkim header.
Useful for debugging purposes.
.It Fl Z
Add all the mail headers to the dkim header.
Useful for debugging purposes.
.El
.Sh SEE ALSO
.Xr smtpd 8