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linux:exim:dkim [2018/04/10 08:32] – created niziaklinux:exim:dkim [2025/06/10 09:48] (current) – [Configure exim4] niziak
Line 1: Line 1:
 +====== DKIM ======
 +
 + RFC 8301 says:
 +
 +rsa-sha1 MUST NOT be used for signing or verifying.
 +
 +Signers MUST use RSA keys of at least 1024 bits for all keys.
 +Signers SHOULD use RSA keys of at least 2048 bits.
 +
 +
 ====== Generate keypair ====== ====== Generate keypair ======
 <code bash> <code bash>
Line 13: Line 23:
 20150726._domainkey.server.com IN TXT "k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC30aRx6rlDA7LkhsM1AtuW8LoBrjo6RZH3yS7nC9EgqV5ntFIzQyCo88hNBz72XwwFAAGKuCVIwcxV06lAHWnUTt+ZyjJlP/4XJo9JH76ZJu9vUTaHw753IY3SZR+xEnJuyBr/LZknAEFqHuDP7V3+B6SWuBElSFFnImnP7oeMQQIDAQAB" 20150726._domainkey.server.com IN TXT "k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC30aRx6rlDA7LkhsM1AtuW8LoBrjo6RZH3yS7nC9EgqV5ntFIzQyCo88hNBz72XwwFAAGKuCVIwcxV06lAHWnUTt+ZyjJlP/4XJo9JH76ZJu9vUTaHw753IY3SZR+xEnJuyBr/LZknAEFqHuDP7V3+B6SWuBElSFFnImnP7oeMQQIDAQAB"
 </code> </code>
 +
 +====== Configure exim4 ======
 +
 +  * In Debian, use **exim4-daemon-heavy** package.
 +  * Change owner of private key file to be readable by exim4. In Debian exim4 user is **Debian-exim**.
 +  * Put private key in */etc/exim4 directory*. In /etc/ssl exim4 cannot find file (chrooted?)
 +remote_smtp transport is running under user 101 (Debian-exim) group 42 (shadow)
 +  * In **exim4.conf** under **remote_smtp** transport add:
 +<code ini>
 +  dkim_canon = relaxed
 +  dkim_selector = 20180410
 +  dkim_domain = spox.org
 +  dkim_private_key = /etc/exim4/dkim.server.com.key
 +#  dkim_strict = true # optional - causes signing failures to defer (requeue)
 +</code>
 +
 +To use DKIM for all sender domains automatically:
 +<code ini>
 +  dkim_domain = ${sender_address_domain}
 +</code>
 +
 +====== References ======
 +
 +  * [[http://takkaria.org/2016/02/dkim-exim-debian|Setting up multi-domain DKIM with exim + Debian]]
 +  * [[https://wiki.sharewiz.net/doku.php?id=exim4:selective_and_multiple_domain_dkim_with_exim|Exim4 - Selective and multiple domain DKIM with Exim]]
 +  * [[https://www.emailonacid.com/blog/article/email-development/what_is_dkim_everything_you_need_to_know_about_digital_signatures|What is DKIM? Everything You Need to Know About Digital Signatures]]
 +
 +
 +
 +====== Tools ======
 +
 +  * [[https://protodave.com/tools/dkim-key-checker/]]