imss:/var/spool/postfix # /usr/sbin/postconf | grep concurrency_limit
default_destination_concurrency_limit = 20
lmtp_destination_concurrency_limit = $default_destination_concurrency_limit
local_destination_concurrency_limit = 2
relay_destination_concurrency_limit = $default_destination_concurrency_limit
smtp_destination_concurrency_limit = $default_destination_concurrency_limit
virtual_destination_concurrency_limit = $default_destination_concurrency_limit