* dovecot: enable login names with square brackets
* config: make IPv4-only relays use self-signed TLS certs
* postfix: make delivery for IP-only relays work
* cmdeploy: skip DNS checks for IPv4 only relays
* www: generate dclogin codes for IPv4-only relays
* opendkim: disable DKIM signing on ipv4-only relays
* get delivery working
* get tests working on IPv4 only machine
* doc: document IPv4-only relays
* dns: warn if mail_domain is an IP, instead of checking DNS
* config: validate domains when formatting them
* ci: add cmlxc testing for no-DNS relays
* ci: run no-dns and normal CI in parallel
* retain "config.mail_domain" as the domain part of @ email addresses, so for ipv4 relays "[1.2.3.4]" and introduce config.ipv4_relay and config.mail_domain_bare helpers.
* ci: migrate from --no-dns to --type ipv4 for cmlxc compatibility
* cleanup dead code, fix docs, fixate cmlxc version
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Co-authored-by: missytake <missytake@systemli.org>
