feat(service-mailbox): the inbound-mail ingest seam — a raw RFC 822 message becomes one sys_mail_message row, associated at ingest, deduplicated, automatic mail suppressed, re-matched on request (stage 1 of #22871)

feat(service-mailbox): the inbound-mail ingest seam — a raw RFC 822 message becomes one sys_mail_message row, associated at ingest, deduplicated, automatic mail suppressed, re-matched on request (stage 1 of #22871) #20355