Problem with Postfix and large mailing list

I have a big problem with Postfix and a large mailing list. My
newsletter is composed by over 70.000 users and some of those users are
using the same mail provider. A lot of them for example (about 4000)
are using hotmail.com.
Some of this big mail providers accept only few concurrently
connections and accept only few recipients (I have seen), I suppose to
avoid spam. So into the maillog I have found a lot of "too many
connections" or "too many recipients". The result was very high e-mails
loss, because Postfix didn't resend these e-mails to the above
providers.

To solve this issue I have changed the Postfix main.cf configuration,
in particular I have modified, in according to the manual, as follows:

smtp_destination_concurrency_limit = 2
smtp_destination_recipient_limit = 2

Naturally this is not a good configuration because my server
performance slow down here as you can imagine! And is not all.
After the previous changing I have notified another strange behaviour.
When Postfix try to send the e-mails to hotmail.com (for example) now I
get a "unknown mail transport error" and the emails goes in deferred
queue.
So I have tried to force the queue and I have enabled verbose logging
for smtp daemon and now it seems send the e-mails. But I cannot
understand the same this issue: why Postfix defers the e-mails only for
those big domains and not for all addresses?
Someone can help me?

This is my postconf output:

access_map_reject_code = 554
address_verify_default_transport = $default_transport
address_verify_local_transport = $local_transport
address_verify_map =
address_verify_negative_cache = yes
address_verify_negative_expire_time = 3d
address_verify_negative_refresh_time = 3h
address_verify_poll_count = 3
address_verify_poll_delay = 3s
address_verify_positive_expire_time = 31d
address_verify_positive_refresh_time = 7d
address_verify_relay_transport = $relay_transport
address_verify_relayhost = $relayhost
address_verify_sender = postmaster
address_verify_service_name = verify
address_verify_transport_maps = $transport_maps
address_verify_virtual_transport = $virtual_transport
alias_database = hash:/etc/aliases, hash:/etc/aliases.majordomo
alias_maps = hash:/etc/aliases, hash:/etc/aliases.majordomo
allow_mail_to_commands = alias, forward
allow_mail_to_files = alias, forward
allow_min_user = no
allow_percent_hack = yes
allow_untrusted_routing = no
alternate_config_directories =
always_bcc =
append_at_myorigin = yes
append_dot_mydomain = yes
application_event_drain_time = 100s
backwards_bounce_logfile_compatibility = yes
berkeley_db_create_buffer_size = 16777216
berkeley_db_read_buffer_size = 131072
best_mx_transport =
biff = yes
body_checks =
body_checks_size_limit = 51200
bounce_notice_recipient = postmaster
bounce_queue_lifetime = 5d
bounce_service_name = bounce
bounce_size_limit = 50000
broken_sasl_auth_clients = no
canonical_maps =
cleanup_service_name = cleanup
command_directory = /usr/sbin
command_expansion_filter =
1234567890!@%-_=+:,./abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWX YZ
command_time_limit = 1000s
config_directory = /etc/postfix
content_filter =
daemon_directory = /usr/libexec/postfix
daemon_timeout = 18000s
debug_peer_level = 2
debug_peer_list =
default_database_type = hash
default_delivery_slot_cost = 5
default_delivery_slot_discount = 50
default_delivery_slot_loan = 3
default_destination_concurrency_limit = 20
default_destination_recipient_limit = 50
default_extra_recipient_limit = 1000
default_minimum_delivery_slots = 3
default_privs = nobody
default_process_limit = 100
default_rbl_reply = $rbl_code Service unavailable; $rbl_class
[$rbl_what] blocked using $rbl_domain${rbl_reason?; $rbl_reason}
default_recipient_limit = 10000
default_transport = smtp
default_verp_delimiters = +=
defer_code = 450
defer_service_name = defer
defer_transports =
delay_notice_recipient = postmaster
delay_warning_time = 0h
deliver_lock_attempts = 20
deliver_lock_delay = 1s
disable_dns_lookups = no
disable_mime_input_processing = no
disable_mime_output_conversion = no
disable_verp_bounces = no
disable_vrfy_command = no
dont_remove = 0
double_bounce_sender = double-bounce
duplicate_filter_limit = 1000
empty_address_recipient = MAILER-DAEMON
enable_errors_to = no
enable_original_recipient = yes
error_notice_recipient = postmaster
error_service_name = error
expand_owner_alias = no
export_environment = TZ MAIL_CONFIG
fallback_relay =
fallback_transport =
fast_flush_domains = $relay_domains
fast_flush_purge_time = 7d
fast_flush_refresh_time = 12h
fault_injection_code = 0
flush_service_name = flush
fork_attempts = 5
fork_delay = 1s
forward_expansion_filter =
1234567890!@%-_=+:,./abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWX YZ
forward_path = $home/.forward${recipient_delimiter}${extension},
$home/.forward
hash_queue_depth = 1
hash_queue_names = incoming, active, deferred, bounce, defer, flush,
hold, trace
header_address_token_limit = 10240
header_checks = regexp:/etc/postfix/header_checks
header_size_limit = 102400
helpful_warnings = yes
home_mailbox = Maildir/
hopcount_limit = 50
html_directory = no
ignore_mx_lookup_error = no
import_environment = MAIL_CONFIG MAIL_DEBUG MAIL_LOGTAG TZ XAUTHORITY
DISPLAY
in_flow_delay = 1s
inet_interfaces = all
initial_destination_concurrency = 5
invalid_hostname_reject_code = 501
ipc_idle = 100s
ipc_timeout = 3600s
ipc_ttl = 1000s
line_length_limit = 2048
lmtp_bind_address =
lmtp_bind_address6 =
lmtp_cache_connection = yes
lmtp_connect_timeout = 0s
lmtp_data_done_timeout = 600s
lmtp_data_init_timeout = 120s
lmtp_data_xfer_timeout = 180s
lmtp_destination_concurrency_limit =
$default_destination_concurrency_limit
lmtp_destination_recipient_limit = $default_destination_recipient_limit
lmtp_lhlo_timeout = 300s
lmtp_mail_timeout = 300s
lmtp_quit_timeout = 300s
lmtp_rcpt_timeout = 300s
lmtp_rset_timeout = 120s
lmtp_sasl_auth_enable = no
lmtp_sasl_password_maps =
lmtp_sasl_security_options = noplaintext, noanonymous
lmtp_send_xforward_command = no
lmtp_skip_quit_response = no
lmtp_tcp_port = 24
lmtp_xforward_timeout = 300s
local_command_shell =
local_destination_concurrency_limit = 2
local_destination_recipient_limit = 1
local_recipient_maps = proxy:unix:passwd.byname $alias_maps
local_transport = local:$myhostname
luser_relay =
mail_name = Postfix
mail_owner = postfix
mail_release_date = 20040915
mail_spool_directory = /var/mail
mail_version = 2.1.5
mailbox_command =
mailbox_command_maps =
mailbox_delivery_lock = fcntl, dotlock
mailbox_size_limit = 51200000
mailbox_transport =
mailq_path = /usr/bin/mailq.postfix
manpage_directory = /usr/share/man
maps_rbl_domains =
maps_rbl_reject_code = 554
masquerade_classes = envelope_sender, header_sender, header_recipient
masquerade_domains =
masquerade_exceptions =
max_idle = 100s
max_use = 100
maximal_backoff_time = 4000s
maximal_queue_lifetime = 5d
message_size_limit = 10240000
mime_boundary_length_limit = 2048
mime_header_checks = $header_checks
mime_nesting_limit = 100
minimal_backoff_time = 1000s
multi_recipient_bounce_reject_code = 550
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
mydomain = programmazione.it
myhostname = postino.programmazione.it
mynetworks = 127.0.0.0/8 212.35.214.80/28 [::1]/128
[fe80::206:29ff:fed5:c7a3]/64
mynetworks_style = subnet
myorigin = $mydomain
nested_header_checks = $header_checks
newaliases_path = /usr/bin/newaliases.postfix
non_fqdn_reject_code = 504
notify_classes = resource, software
owner_request_special = yes
parent_domain_matches_subdomains =
debug_peer_list,fast_flush_domains,mynetworks,perm it_mx_backup_networks,qmqpd_authorized_clients,rel ay_domains,smtpd_acces
s_maps
permit_mx_backup_networks =
pickup_service_name = pickup
prepend_delivered_header = command, file, forward
process_id_directory = pid
propagate_unmatched_extensions = canonical, virtual
proxy_interfaces =
proxy_read_maps = $local_recipient_maps $mydestination
$virtual_alias_maps $virtual_alias_domains $virtual_mailbox_maps
$virtual_mailbox_domains $relay_recip
ient_maps $relay_domains $canonical_maps $sender_canonical_maps
$recipient_canonical_maps $relocated_maps $transport_maps $mynetworks
qmgr_clog_warn_time = 300s
qmgr_fudge_factor = 100
qmgr_message_active_limit = 20000
qmgr_message_recipient_limit = 20000
qmgr_message_recipient_minimum = 10
qmqpd_authorized_clients =
qmqpd_error_delay = 1s
qmqpd_timeout = 300s
queue_directory = /var/spool/postfix
queue_file_attribute_count_limit = 100
queue_minfree = 0
queue_run_delay = 500s
queue_service_name = qmgr
rbl_reply_maps =
readme_directory = /usr/share/doc/postfix-2.1.5/README_FILES
receive_override_options =
recipient_bcc_maps =
recipient_canonical_maps =
recipient_delimiter =
reject_code = 554
relay_clientcerts =
relay_destination_concurrency_limit =
$default_destination_concurrency_limit
relay_destination_recipient_limit =
$default_destination_recipient_limit
relay_domains = $mydestination
relay_domains_reject_code = 554
relay_recipient_maps =
relay_transport = relay
relayhost =
relocated_maps =
require_home_directory = no
resolve_dequoted_address = yes
resolve_null_domain = no
rewrite_service_name = rewrite
sample_directory = /usr/share/doc/postfix-2.1.5/samples
sender_based_routing = no
sender_bcc_maps =
sender_canonical_maps =
sendmail_path = /usr/sbin/sendmail.postfix
service_throttle_time = 60s
setgid_group = postdrop
show_user_unknown_table_name = yes
showq_service_name = showq
smtp_always_send_ehlo = yes
smtp_bind_address =
smtp_bind_address6 =
smtp_connect_timeout = 30s
smtp_data_done_timeout = 600s
smtp_data_init_timeout = 120s
smtp_data_xfer_timeout = 180s
smtp_defer_if_no_mx_address_found = no
smtp_destination_concurrency_limit = 22
smtp_destination_recipient_limit = 2
smtp_enforce_tls = no
smtp_helo_name = $myhostname
smtp_helo_timeout = 300s
smtp_host_lookup = dns
smtp_line_length_limit = 990
smtp_mail_timeout = 300s
smtp_mx_address_limit = 0
smtp_mx_session_limit = 2
smtp_never_send_ehlo = no
smtp_pix_workaround_delay_time = 10s
smtp_pix_workaround_threshold_time = 500s
smtp_quit_timeout = 300s
smtp_quote_rfc821_envelope = yes
smtp_randomize_addresses = yes
smtp_rcpt_timeout = 300s
smtp_rset_timeout = 120s
smtp_sasl_auth_enable = no
smtp_sasl_password_maps =
smtp_sasl_security_options = noplaintext, noanonymous
smtp_sasl_tls_security_options = $var_smtp_sasl_opts
smtp_sasl_tls_verified_security_options = $var_smtp_sasl_tls_opts
smtp_send_xforward_command = no
smtp_skip_5xx_greeting = yes
smtp_skip_quit_response = yes
smtp_starttls_timeout = 300s
smtp_tls_CAfile =
smtp_tls_CApath =
smtp_tls_cert_file =
smtp_tls_cipherlist =
smtp_tls_dcert_file =
smtp_tls_dkey_file = $smtp_tls_dcert_file
smtp_tls_enforce_peername = yes
smtp_tls_key_file = $smtp_tls_cert_file
smtp_tls_loglevel = 0
smtp_tls_note_starttls_offer = no
smtp_tls_per_site =
smtp_tls_scert_verifydepth = 5
smtp_tls_session_cache_database =
smtp_tls_session_cache_timeout = 3600s
smtp_use_tls = no
smtp_xforward_timeout = 300s
smtpd_authorized_verp_clients = $authorized_verp_clients
smtpd_authorized_xclient_hosts =
smtpd_authorized_xforward_hosts =
smtpd_banner = $myhostname ESMTP $mail_name
smtpd_client_connection_count_limit = 50
smtpd_client_connection_limit_exceptions = $mynetworks
smtpd_client_connection_rate_limit = 0
smtpd_client_restrictions = reject_rbl_client zombie.dnsbl.sorbs.net,
reject_rbl_client relays.ordb.org, reject_rbl_client opm.blitzed.org,
reject_rbl_cli
ent list.dsbl.org, reject_rbl_client sbl.spamhaus.org, permit
smtpd_data_restrictions =
smtpd_delay_reject = yes
smtpd_enforce_tls = no
smtpd_error_sleep_time = 1s
smtpd_etrn_restrictions =
smtpd_expansion_filter =
\t\40!"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~
smtpd_hard_error_limit = 20
smtpd_helo_required = no
smtpd_helo_restrictions =
smtpd_history_flush_threshold = 100
smtpd_junk_command_limit = 100
smtpd_noop_commands =
smtpd_null_access_lookup_key = <>
smtpd_policy_service_max_idle = 300s
smtpd_policy_service_max_ttl = 1000s
smtpd_policy_service_timeout = 100s
smtpd_proxy_ehlo = $myhostname
smtpd_proxy_filter =
smtpd_proxy_timeout = 100s
smtpd_recipient_limit = 1000
smtpd_recipient_overshoot_limit = 1000
smtpd_recipient_restrictions = permit_mynetworks,
reject_non_fqdn_recipient, reject_unauth_destination,
regexp:/etc/postfix/access_regexp, permit
smtpd_reject_unlisted_recipient = yes
smtpd_reject_unlisted_sender = no
smtpd_restriction_classes =
smtpd_sasl_application_name = smtpd
smtpd_sasl_auth_enable = no
smtpd_sasl_exceptions_networks =
smtpd_sasl_local_domain =
smtpd_sasl_security_options = noanonymous
smtpd_sasl_tls_security_options = $smtpd_sasl_security_options
smtpd_sender_login_maps =
smtpd_sender_restrictions = check_sender_access
hash:/etc/postfix/sender_access, reject_non_fqdn_sender, permit
smtpd_soft_error_limit = 10
smtpd_starttls_timeout = 300s
smtpd_timeout = 300s
smtpd_tls_CAfile =
smtpd_tls_CApath =
smtpd_tls_ask_ccert = no
smtpd_tls_auth_only = no
smtpd_tls_ccert_verifydepth = 5
smtpd_tls_cert_file =
smtpd_tls_cipherlist =
smtpd_tls_dcert_file =
smtpd_tls_dh1024_param_file =
smtpd_tls_dh512_param_file =
smtpd_tls_dkey_file = $smtpd_tls_dcert_file
smtpd_tls_key_file = $smtpd_tls_cert_file
smtpd_tls_loglevel = 0
smtpd_tls_received_header = no
smtpd_tls_req_ccert = no
smtpd_tls_session_cache_database =
smtpd_tls_session_cache_timeout = 3600s
smtpd_tls_wrappermode = no
smtpd_use_tls = no
soft_bounce = no
stale_lock_time = 500s
strict_7bit_headers = no
strict_8bitmime = no
strict_8bitmime_body = no
strict_mime_encoding_domain = no
strict_rfc821_envelopes = no
sun_mailtool_compatibility = no
swap_bangpath = yes
syslog_facility = mail
syslog_name = postfix
tls_daemon_random_bytes = 32
tls_daemon_random_source =
tls_ipv6_version = 1.25
tls_random_bytes = 32
tls_random_exchange_name = ${config_directory}/prng_exch
tls_random_prng_update_period = 60s
tls_random_reseed_period = 3600s
tls_random_source =
trace_service_name = trace
transport_maps =
transport_retry_time = 60s
trigger_timeout = 10s
undisclosed_recipients_header = To: undisclosed-recipients:;
unknown_address_reject_code = 450
unknown_client_reject_code = 450
unknown_hostname_reject_code = 450
unknown_local_recipient_reject_code = 550
unknown_relay_recipient_reject_code = 550
unknown_virtual_alias_reject_code = 550
unknown_virtual_mailbox_reject_code = 550
unverified_recipient_reject_code = 450
unverified_sender_reject_code = 450
verp_delimiter_filter = -=+
virtual_alias_domains = $virtual_alias_maps
virtual_alias_expansion_limit = 1000
virtual_alias_maps = $virtual_maps
virtual_alias_recursion_limit = 1000
virtual_destination_concurrency_limit =
$default_destination_concurrency_limit
virtual_destination_recipient_limit =
$default_destination_recipient_limit
virtual_gid_maps =
virtual_mailbox_base =
virtual_mailbox_domains = $virtual_mailbox_maps
virtual_mailbox_limit = 51200000
virtual_mailbox_lock = fcntl
virtual_mailbox_maps =
virtual_minimum_uid = 100
virtual_transport = virtual
virtual_uid_maps =