One ISP (french isp Orange) blocks emails from my server : Too many connections, slow down. OFR004_104 [104] I have read some doc about "smtp_destination_concurrency_limit": /etc/postfix/master.cf: slow inet n - - - - smtpd /etc/postfix/transports: domain1.com slow: domain2.com slow: /etc/postfix/main.cf: slow_destination_concurrency_limit = 10 slow_destination_rate_delay = 40s But it doesn't work! How can i do to act over a domain ?