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.\" Copyright (c) 2019 Martijn van Duren <martijn@openbsd.org>
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.Dd $Mdocdate$
.Dt FILTER-DKIMSIGN 8
.Os
.Sh NAME
.Nm filter-dkimsign
.Nd add dkim signature to messages
.Sh SYNOPSIS
.Nm
.Op Fl tz
.Op Fl a Ar algorithm
.Op Fl c Ar canonicalization
.Op Fl h Ar headers
.Op Fl x Ar seconds
.Fl d Ar domain
.Fl D Ar file
.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 Ar algorithm
The
.Ar algorithm
to use.
Supported signing algorithms are
.Em rsa
and
.Em ed25519 Pq when enabled at compile time .
Only sha256 should be used for hashing, since other algorithms are most likely
not supported by verifiers.
Defaults to
.Cm rsa-sha256 .
.It Fl c Ar canonicalization
The canonicalization algorithm used to sign the message.
Defaults to
.Em simple/simple .
.It Fl D Ar file
.Ar file
should point to a file containing a list of domains.
Only one domain per line should be specified.
See
.Fl d
for more information.
.It Fl d Ar domain
The
.Ar domain
where the public key can be found.
This option can be specified multiple times to select the best
.Ar domain
during signing.
If specified multiple times it looks at the domain component of the first
mailbox in the from-header and tries to find a match.
If no exact match can be found it looks for the closest parent
.Ar domain .
If no matches can be the first
.Ar domain
specified will be used.
.It Fl h Ar headers
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
.Em 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
.Ar file
should point to a file containing the RSA private key to sign the messages.
.It Fl s Ar selector
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 Ar seconds
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.
If a second
.Fl z
is specified all headers will be included in the dkim header.
Useful for debugging purposes.
.El
.Sh SEE ALSO
.Xr smtpd 8
.Sh STANDARDS
.Rs
.%A D. Crocker, Ed.
.%Q Brandenburg InternetWorking
.%A T. Hansen, Ed.
.%Q AT&T Laboratories
.%A M. Kucherawy, Ed.
.%Q Cloudmark
.%D September 2011
.%R RFC 6376
.%T DomainKeys Identified Mail (DKIM) Signatures
.Re
.Pp
.Rs
.%A J. Levine
.%Q Taughannock Networks
.%D September 2018
.%R RFC 8463
.%T A New Cryptographic Signature Method for DomainKeys Identified Mail
.Re
.Sh AUTHORS
.An Martijn van Duren Aq Mt martijn@openbsd.org