Exclude Mailcow-managed domains from newly registered domain URI checks

Summary

Mailcow-managed domains can currently trigger newly registered domain URI checks such as SEM_URIBL_FRESH15 when the domain appears in the body of an incoming email.

Since Mailcow already knows which domains are configured locally, it would be useful to exclude those domains from domain-age-based URI/RBL checks such as Fresh15 (and potentially similar checks such as Spamhaus ZRD).

This should ideally be limited to checks whose purpose is detecting newly registered domains rather than globally whitelisting local domains from all URI reputation checks.

Motivation

When a newly registered domain is added to Mailcow and used for mailboxes, incoming messages that mention that domain in their body can receive a significant spam score simply because the domain itself is new.

For example, Rspamd may add:

SEM_URIBL_FRESH15 (3) [example.com:email]

This can happen with perfectly legitimate messages containing links, signatures, quoted replies, or email addresses using the locally configured domain.

In this situation, the "newly registered domain" signal provides little useful information: Mailcow already knows that the domain belongs to the local installation and why it is newly registered.

Mailcow already exposes its configured domains to Rspamd via DOMAIN_MAP, so it seems possible to use that information to selectively skip age-based domain reputation checks for local domains.

Automatically adding local domains to the general SURBL whitelist would be less desirable, since ownership of a mail domain does not necessarily imply that all web content hosted under that domain is trustworthy. A targeted exclusion for newly registered/domain-age checks would preserve other useful URI reputation and security checks.

Additional context

No response