More tips on tunning postfix

These are from python.org server

default_destination_concurrency_limit=50
default_destination_recipient_limit=50
default_process_limit=200
smtp_mx_session_limit=100
smtpd_client_connection_count_limit=100
smtp_destination_concurrency_limit=100
maximal_backoff_time = 1000s
minimal_backoff_time = 300s