Mail queue filling up, delivery real slow

mail server is: 10.4.2 running on a dual 2 GHz Xserve 1 gig RAM
2 hard drives. 1 boot, 1 mail store

my mail queue is filling up with messages that can’t be delivered. bad address usually. not sure why they make into the queue in the first place.
The queue reaches as high a 7000+ messages.
This is really killing my server. Can anyone shed some light??

here is postconf output:
alias_maps = hash:/etc/aliases,hash:/var/mailman/data/aliases
always_bcc =
bounce_queue_lifetime = 4h
command_directory = /usr/sbin
config_directory = /etc/postfix
content_filter = smtp-amavis:[127.0.0.1]:10024
daemon_directory = /usr/libexec/postfix
debug_peer_level = 2
default_destination_concurrency_limit = 6
default_process_limit = 20
enable_server_options = yes
inet_interfaces = all
initial_destination_concurrency = 15
local_recipient_maps =
luser_relay = emailadmin
mail_owner = postfix
mailbox_size_limit = 0
mailbox_transport = cyrus
mailq_path = /usr/bin/mailq
manpage_directory = /usr/share/man
maps_rbl_domains =
maximal_backoff_time = 2700s
maximal_queue_lifetime = 36h
message_size_limit = 16777216
minimal_backoff_time = 900s
mydestination = $myhostname,localhost.$mydomain,myDomain.com
mydomain_fallback = localhost
myhostname = thestranger.com
mynetworks = 127.0.0.1/32,10.0.0.0/24,10.0.8.0/24,10.0.1.0/24
mynetworks_style = host
newaliases_path = /usr/bin/newaliases
owner_request_special = no
queue_directory = /private/var/spool/postfix
queue_run_delay = 900s
readme_directory = /usr/share/doc/postfix
recipient_delimiter = +
relayhost =
sample_directory = /usr/share/doc/postfix/examples
sendmail_path = /usr/sbin/sendmail
setgid_group = postdrop
smtp_connect_timeout = 15s
smtp_helo_timeout = 30s
smtpd_client_restrictions = check_recipient_access hash:/etc/postfix/access, permit_sasl_authenticated, permit_mynetworks, check_sender_access hash:/etc/postfix/whiteList, reject_invalid_hostname, reject_non_fqdn_sender, reject_non_fqdn_recipient, reject_rbl_client dnsbl.njabl.org, reject_rbl_client sbl-xbl.spamhaus.org, reject_rbl_client bl.spamcop.net, reject_rbl_client cbl.abuseat.org
smtpd_enforce_tls = no
smtpd_pw_server_security_options = login,plain,cram-md5,gssapi
smtpd_recipient_restrictions = check_recipient_access hash:/etc/postfix/access, permit_mynetworks, permit_sasl_authenticated, reject_invalid_hostname, reject_non_fqdn_sender, reject_non_fqdn_recipient, reject_unknown_sender_domain, reject_unauth_destination, check_sender_access hash:/etc/postfix/whiteList
smtpd_sasl_auth_enable = yes
smtpd_tls_cert_file = /etc/certificates/myDomain.com.crt
smtpd_tls_key_file = /etc/certificates/myDomain.com.key
smtpd_tls_loglevel = 2
smtpd_use_pw_server = yes
smtpd_use_tls = yes
unknown_local_recipient_reject_code = 550
virtual_alias_maps = hash:/etc/postfix/virtual,hash:/var/mailman/data/virtual-mailman
virtual_mailbox_domains = hash:/etc/postfix/virtual_domains
virtual_transport = lmtp:unix:/Volumes/Mail/imap/socket/lmtp