I asked a very similar question some 4 or 5 months ago, but haven't tracked down a suitable answer. I decided to post a new question so that I can ... a) Post updated info b) post my most current postconf -n output

When a user sends mail from inside the network (via webmail) to email addresses both inside and outside the network, the email is delivered. When a user with an email account on the system sends mail from outside the network, using the server as the relay, to addresses inside the network, the email is delivered.

But [sometimes] when a user connects via SMTPD to send email to an external address, a Relay Access Denied error is returned:

Feb 25 19:33:49 myers postfix/smtpd[8044]: NOQUEUE: reject: RCPT from host-68-169-158-182.WISOLT2.epbfi.com[68.169.158.182]: 554 5.7.1 <host-68-169-158-182.WISOLT2.epbfi.com[68.169.158.182]>: Client host rejected: Access denied; from=<[email protected]> to=<[email protected]> proto=ESMTP helo=<my-computer-name>
Feb 25 19:33:52 myers postfix/smtpd[8044]: disconnect from host-68-169-158-182.WISOLT2.epbfi.com[68.169.158.182]

Sending this through Microsoft Outlook 2003 generates the above log. However, sending through my iPhone, with the exact same settings, goes through fine:

Feb 25 19:37:18 myers postfix/qmgr[3619]: A2D861302C9: from=<[email protected]>, size=1382, nrcpt=1 (queue active)
Feb 25 19:37:18 myers amavis[2799]: (02799-09) FWD via SMTP: <[email protected]> -> <[email protected]>,BODY=7BIT 250 2.0.0 Ok, id=02799-09, from MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as A2D861302C9
Feb 25 19:37:18 myers amavis[2799]: (02799-09) Passed CLEAN, [68.169.158.182] [68.169.158.182] <[email protected]> -> <[email protected]>, Message-ID: <[email protected]>, mail_id: yMLvzVQJloFV, Hits: -9.607, size: 897, queued_as: A2D861302C9, 6283 ms
Feb 25 19:37:18 myers postfix/lmtp[8752]: 2ED3A1302C8: to=<[email protected]>, relay=127.0.0.1[127.0.0.1]:10024, delay=6.6, delays=0.25/0.01/0.19/6.1, dsn=2.0.0, status=sent (250 2.0.0 Ok, id=02799-09, from MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as A2D861302C9)
Feb 25 19:37:18 myers postfix/qmgr[3619]: 2ED3A1302C8: removed

Outgoing Settings on Outlook 2003 match the settings on my iPhone: SMTP server: mail.my-domain.com Username: My full email address Uses SSL Server Port 587

Now, here's postconf -n. I realize the "My Networks" Parameter is a bit nasty. I have these IP addresses in here for just this reason, as others have been complaining of this problem too:

alias_database = hash:/etc/postfix/aliases
alias_maps = $alias_database
append_dot_mydomain = no
biff = no
broken_sasl_auth_clients = yes
command_directory = /usr/sbin
config_directory = /etc/postfix
content_filter = amavisfeed:[127.0.0.1]:10024
daemon_directory = /usr/libexec/postfix
debug_peer_level = 2
disable_vrfy_command = yes
html_directory = no
inet_interfaces = all
mail_owner = postfix
mail_spool_directory = /var/spool/mail
mailbox_size_limit = 0
mailq_path = /usr/bin/mailq
manpage_directory = /usr/share/man
message_size_limit = 20480000
mydestination = $myhostname, localhost, localhost.$mydomain
mydomain = my-domain.com
myhostname = myers.my-domain.com
mynetworks = 127.0.0.0/8, 74.125.113.27, 74.125.82.49, 74.125.79.27, 209.85.161.0/24, 209.85.214.0/24, 209.85.216.0/24, 209.85.212.0/24, 209.85.160.0/24
myorigin = $myhostname
newaliases_path = /usr/bin/newaliases
queue_directory = /var/spool/postfix
readme_directory = /usr/share/doc/postfix-2.3.3/README_FILES
receive_override_options = no_address_mappings
recipient_delimiter = +
relay_domains = $mydestination
sample_directory = /usr/share/doc/postfix-2.3.3/samples
sendmail_path = /usr/sbin/sendmail
setgid_group = postdrop
smtp_bind_address = my-primary-server's IP address
smtpd_banner = mail.my-domain.com
smtpd_helo_required = yes
smtpd_sasl_auth_enable = yes
smtpd_sasl_path = private/auth
smtpd_sasl_type = dovecot
smtpd_tls_auth_only = yes
smtpd_tls_cert_file = /etc/ssl/mailserver/postfix.pem
smtpd_tls_key_file = /etc/ssl/mailserver/private/postfix.pem
smtpd_tls_loglevel = 3
smtpd_tls_received_header = no
smtpd_tls_session_cache_timeout = 3600s
smtpd_use_tls = yes
tls_random_source = dev:/dev/urandom
unknown_local_recipient_reject_code = 554
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf,mysql:/etc/postfix/mysql-email2email.cf
virtual_gid_maps = static:5000
virtual_mailbox_base = /var/vmail
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_minimum_uid = 5000
virtual_transport = dovecot
virtual_uid_maps = static:5000

If anyone has any ideas and can help me finally solve this issue once and for all, I'd be eternally grateful.