---
name: "Mail::SpamAssassin::RegistryBoundaries"
section: "3pm"
platform: "linux"
package: "spamassassin"
version: "4.0.2-3"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/Mail::SpamAssassin::RegistryBoundaries"
---

# Mail::SpamAssassin::RegistryBoundaries(3pm)

domain delegation rules

## NAME

Mail::SpamAssassin::RegistryBoundaries - domain delegation rules

## METHODS

- ($hostname, $domain) = split\_domain ($fqdn, $is\_ascii)

  Cut a fully-qualified hostname into the hostname part and the domain part, splitting at the DNS registry boundary.

  Examples:

  ```
      "www.foo.com" => ( "www", "foo.com" )
      "www.foo.co.uk" => ( "www", "foo.co.uk" )
  ```

  If `$is_ascii` given and true, skip **idn\_to\_ascii()** conversion

- $domain = trim\_domain($fqdn, $is\_ascii)

  Cut a fully-qualified hostname into the hostname part and the domain part, returning just the domain.

  Examples:

  ```
      "www.foo.com" => "foo.com"
      "www.foo.co.uk" => "foo.co.uk"
  ```

  If `$is_ascii` given and true, skip **idn\_to\_ascii()** conversion

- $ok = is\_domain\_valid($dom, $is\_ascii)

  Return `1` if the domain/hostname uses valid known TLD, `"undef"` otherwise.

  If `$is_ascii` given and true, skip **idn\_to\_ascii()** conversion.

  Note that this only checks the TLD validity and nothing else.  To verify that the complete fqdn is in a valid legal format, **Util::is\_fqdn\_valid()** can additionally be used.