feat(everinbox): add subdomain sending templates

[gbretas]

Description

Adds subdomain sending support for Everinbox templates. When customers send email from a subdomain (e.g. marketing.example.com) rather than the root domain, the existing templates place DKIM, DMARC and mail routing records under the root zone — causing DKIM verification failures.

New templates:

• everinbox.domain-auth-subdomain — DKIM + DMARC + mail routing for subdomain sending domains
• everinbox.domain-auth-tracking-subdomain — same as above + URL/click tracking CNAME

Updated template:

• everinbox.domain-auth-tracking bumped to version 2 — consolidated two tracking CNAMEs (URL_TRACKING + CLICK_TRACKING) into a single TRACKING_SUBDOMAIN/TRACKING_TARGET pair, matching real-world usage

Why %SUBDOMAIN% in host instead of the host parameter:
Cloudflare — the primary DNS provider for our users — explicitly does not support the Domain Connect host parameter (it is ignored per their documentation). Using %SUBDOMAIN% as a variable in the host field is the only viable workaround for providers that do not implement this part of the spec. The non-variable parts of each host are fixed (._domainkey., _dmarc., em*.) to limit misuse, consistent with the spirit of the quality guideline.

Type of change

• New template
• New feature (non-breaking change which adds functionality to the template)
• Breaking change (fix or feature that would cause existing template behavior to be not backward compatible) — domain-auth-tracking v2 renames tracking variables

How Has This Been Tested?

• Template functionality checked using Online Editor
• Template file name follows the pattern <providerId>.<serviceId>.json
• resource URL provided with logoUrl is actually served by a webserver

Checklist of common problems

• syncPubKeyDomain is set — present on all templates
• warnPhishing is not set alongside syncPubKeyDomain — warnPhishing: false on all templates
• syncRedirectDomain is set whenever the template uses redirect_uri in the synchronous flow
• no TXT record contains SPF content — DMARC uses TXT with v=DMARC1, not SPF
• txtConflictMatchingMode is set on every TXT record that must be unique — set to "All" on DMARC record
• no variable is used as a bare full record value — all variables are combined with fixed text
• no bare variable is used as the full host label — all host labels contain fixed parts (e.g. %DKIM_SELECTOR1%._domainkey.%SUBDOMAIN%)
• %host% does not appear explicitly in any host attribute
• essential is set to OnApply on records the end user may need to modify — set on DMARC record

Note on %SUBDOMAIN% in host: The guideline recommends using the host parameter instead of a variable in the host field to create a subdomain. However, Cloudflare (our primary provider) explicitly ignores the host parameter in their Domain Connect implementation. The %SUBDOMAIN% variable is therefore the only working solution for subdomain scoping on Cloudflare. All other host parts remain fixed.

Online Editor test results

Editor test link(s):

Test everinbox/domain-auth-subdomain example.com/@

Note: editor test link for everinbox.domain-auth-tracking-subdomain uses the same variable structure; separate link available on request.

[github-actions]

✅ JSON Filename Check Passed

[github-actions]

✅ JSON Schema Validation Passed

[github-actions]

Linter OK

everinbox.domain-auth-subdomain.json

Level	Code	Note

everinbox.domain-auth-tracking-subdomain.json

Level	Code	Note

everinbox.domain-auth-tracking.json

Level	Code	Note

[github-actions]

PR Description Check Failed

The PR description is missing required elements. Please update it according to the PR template.

Details

  WARNING: could not decode token: Incorrect padding
  OK  Type of change: 3/3 checkboxes ticked
  OK  How Has This Been Tested?: all 3 checkboxes ticked
  OK  Checklist of common problems: 9/9 checkboxes ticked

Labels to add: Test links missing
Labels to remove: Checklist of common problems not complete, Forged editor links, PR description incomplete

PR description check FAILED:
  FAIL  'Online Editor test results': no valid editor test link found
  FAIL  Template coverage: everinbox.domain-auth-subdomain.json: no editor test link found (expected template id 'everinbox.domain-auth-subdomain')
  FAIL  Template coverage: everinbox.domain-auth-tracking-subdomain.json: no editor test link found (expected template id 'everinbox.domain-auth-tracking-subdomain')
  FAIL  Template coverage: everinbox.domain-auth-tracking.json: no editor test link found (expected template id 'everinbox.domain-auth-tracking')