Você pode usar o truque de erros:
main.cf:
transport_maps = hash:/etc/postfix/transport
deadbeats_destination_concurrency_limit = 50
master.cf:
deadbeats unix - - n - - smtp -o smtp_connect_timeout=5 -o smtp_helo_timeout=5 smtp_connect_timeout=2
transport.cf:
hotmail.com deadbeats:
yahoo.com deadbeats:
earthlink.net deadbeats:
freemail.com.au deadbeats: