"""Shared recipient-domain exclusions for outbound cold-email campaigns.

We self-host our MTA (transactional relays like SES forbid cold email), so we
must protect our sending-IP reputation manually. The single biggest lever is
NOT mailing the Yahoo/Verizon-Media family: those providers aggressively defer
cold senders with "unexpected volume / user complaints" 421 responses, which
poisons the IP for every other provider too.

Keep this list authoritative and import it everywhere we build audiences.
"""

from __future__ import annotations

# Yahoo / Verizon Media operates ALL of these consumer domains. Legacy AT&T and
# Frontier consumer mail was handed off to Yahoo's infrastructure as well.
YAHOO_FAMILY_DOMAINS: frozenset[str] = frozenset({
    # Yahoo / AOL core
    "yahoo.com", "yahoo.com.mx", "yahoo.es", "yahoo.it", "yahoo.ca",
    "myyahoo.com", "ymail.com", "rocketmail.com",
    "aol.com", "aol.com.mx", "aim.com", "love.com", "games.com", "wow.com",
    "netscape.net", "netscape.com", "cs.com", "compuserve.com",
    # AT&T family (Yahoo-hosted)
    "att.net", "sbcglobal.net", "bellsouth.net", "pacbell.net",
    "ameritech.net", "swbell.net", "snet.net", "flash.net", "prodigy.net",
    "wans.net", "nvbell.net",
    # Verizon family (Yahoo-hosted)
    "verizon.net", "verizongni.com", "bellatlantic.net",
    # Frontier (Yahoo-hosted)
    "frontier.com", "frontiernet.net",
})

# The full set of consumer domains we refuse to cold-mail. Extend here as we
# discover other reputation-sensitive providers.
BLOCKED_EMAIL_DOMAINS: frozenset[str] = YAHOO_FAMILY_DOMAINS


def domain_of(email: str) -> str:
    """Return the lowercased domain part of an email, or '' if malformed."""
    if "@" not in email:
        return ""
    return email.rsplit("@", 1)[-1].strip().lower()


def is_blocked(email: str) -> bool:
    return domain_of(email) in BLOCKED_EMAIL_DOMAINS