docs: Combine DKIM/DMARC/SPF pages (docker-mailserver#3231)

Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>

Author: georglauterbach

docs/content/config/advanced/optional-config.md

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-This is a list of all configuration files and directories which are optional or automatically generated in your `docker-data/dms/config/` directory.
+This is a list of all configuration files and directories which are optional or automatically generated in your `docker-data/dms/config/` directory. We use this path to reference the local config directory in our docs, which you should attach a volume into the container at `/tmp/docker-mailserver`.
 
 ## Directories
 
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 [docs-accounts-quota]: ../../config/user-management.md#quotas
 [docs-aliases-regex]: ../../config/user-management.md#configuring-regexp-aliases
-[docs-dkim]: ../../config/best-practices/dkim.md
+[docs-dkim]: ../../config/best-practices/dkim_dmarc_spf.md#dkim
 [docs-fail2ban]: ../../config/security/fail2ban.md
 [docs-faq-spamrules]: ../../faq.md#how-can-i-manage-my-custom-spamassassin-rules
 [docs-faq-userpatches]: ../../faq.md#how-to-adjust-settings-with-the-user-patchessh-script

docs/content/config/best-practices/autodiscover.md

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+# Auto-Discovery of Services
+
 Email auto-discovery means a client email is able to automagically find out about what ports and security options to use, based on the mail-server URI. It can help simplify the tedious / confusing task of adding own's email account for non-tech savvy users.
 
 Email clients will search for auto-discoverable settings and prefill almost everything when a user enters its email address :heart: