opensmtpd-filter-dkimsign

dkim signer integration to the OpenSMTPD daemon

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  1. Package version
    opensmtpd-filter-dkimsign-0.5p2
  2. Maintainer
    Martijn van Duren

filter-dkim is an opensmtpd filter that signs email with a dkim signature.

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| Running ${PKGSTEM} on OpenBSD
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To use filter-dkimsign, you must first generate a private key:

doas -u _dkimsign openssl genrsa -out ${SYSCONFDIR}/mail/dkim/private.rsa.key 2048

To generate the public key ready for dns:

openssl rsa -in ${SYSCONFDIR}/mail/dkim/private.rsa.key -pubout | \
sed '1s/.*/v=DKIM1;p=/;:nl;${s/-----.*//;q;};N;s/\n//g;b nl;'

This value needs to be placed in a DNS txt record with the following syntax:
<selector>._domainkey.<domain>

Edit the /etc/mail/smtpd.conf file to declare the filter:

filter dkimsign_rsa proc-exec "filter-dkimsign -d <domain> -s <selector> -k ${SYSCONFDIR}/mail/dkim/private.rsa.key" user _dkimsign group _dkimsign

Then add the filter to each listener that should be signed:

listen on all filter dkimsign_rsa

To use Ed25519 similar steps must be taken.

To generate the private key:

doas -u _dkimsign openssl genpkey -algorithm ed25519 -outform PEM -out ${SYSCONFDIR}/mail/dkim/private.ed25519.key

To generate the public key ready for dns:

printf "v=DKIM1;k=ed25519;p=%s\n" "$(doas -u _dkimsign openssl pkey -outform DER -pubout -in ${SYSCONFDIR}/mail/dkim/private.ed25519.key | tail -c +13 | openssl base64)"

Edit the /etc/mail/smtpd.conf file to declare the filter:

filter dkimsign_ed25519 proc-exec "filter-dkimsign -a ed25519-sha256 -d <domain> -s <selector> -k ${SYSCONFDIR}/mail/dkim/private.ed25519.key" user _dkimsign group _dkimsign

To add both filters to each listener that should be signed:

filter dkimsign chain { dkimsign_rsa, dkimsign_ed25519 }
listen on all filter dkimsign

For a full list of options see filter-dkimsign(8).