[postfix-jp: 4362] ããååãããããéäãããdeferred (lost connection with ... while sending message body)

[yasuhara <yasuhara@xxxxxxxxxxxxxxxx>]

やすはらと申します。
Postfixバージョンは、2.3.3 になります。

ある特定の宛先アドレスに、添付ファイル付きメールを送信した場合、

... status=deferred (lost connection with mx.example.jp[yyy.yyy.yyy.yyy] 
while sending message body)
... status=deferred (conversation with mx.example.jp[yyy.yyy.yyy.yyy] 
timed out while sending MAIL FROM)
... status=deferred (lost connection with mx.example.jp[yyy.yyy.yyy.yyy] 
while performing the HELO handshake)

等の失敗を繰り返し、

約１１間後のトライで、やっと　status=sent　になる相手先があります。

この場合、考えられる原因は何でしょうか？
こちらのPostfix の設定で、改善することは出来ますでしょうか？

よろしくお願いいたします。

■補足
]# postconf -n
alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
command_directory = /usr/sbin
config_directory = /etc/postfix
daemon_directory = /usr/libexec/postfix
debug_peer_level = 2
home_mailbox = Maildir/
html_directory = no
inet_interfaces = all
mail_owner = postfix
mailbox_command = /usr/bin/procmail
mailbox_size_limit = 204800000
mailq_path = /usr/bin/mailq.postfix
manpage_directory = /usr/share/man
message_size_limit = 102400000
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain, 
web.example.co.jp
mydomain = example.co.jp
myhostname = smtp.example.co.jp
myorigin = $mydomain
newaliases_path = /usr/bin/newaliases.postfix
queue_directory = /var/spool/postfix
readme_directory = /usr/share/doc/postfix-2.3.3/README_FILES
sample_directory = /usr/share/doc/postfix-2.3.3/samples
sendmail_path = /usr/sbin/sendmail.postfix
setgid_group = postdrop
smtp_helo_name = $myhostname
smtpd_banner = $myhostname ESMTP unknown
smtpd_client_restrictions = 
permit_mynetworks,                            permit
smtpd_recipient_restrictions = permit_mynetworks 
permit_sasl_authenticated    reject_unauth_destination
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain = $myhostname
unknown_local_recipient_reject_code = 550
virtual_alias_maps = hash:/etc/postfix/virtual
以上。

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