The Jun 13-14 Gmail+Outlook block storm came from the main/trucking pool having
NO per-MX throttling (only HC had it) -- it concentrated warmup volume on
Google/Microsoft-Workspace-hosted business domains. Port the HC fix:
- migration 097: fmcsa_carriers.mx_provider column.
- mx_tag_carriers.py: resolve MX once per distinct domain (reuses the verifier's
classifier+cache), tag every carrier with that domain's operator. Bounded per
run, prioritizes unsent verified carriers.
- build_trucking_campaigns: during warmup (day<=6) EXCLUDE tagged Google/MS/
Proofpoint/etc. carriers in fetch_carriers; per-MX cap in select_sendable_
carriers so known operators never dominate the quota. Untagged carriers pass
(not collapsed onto one bucket) until tagging fills in. mx_daily_caps ramps
with the main warmup day; MAIN_SKIP_BIG_MX=0 disables once warmed.
