Some SMTP connections to Symantec Messaging Gateway (SMG) are being deferred even though the connecting IP address is in the Local Good Sender IP list (found in Reputation > Good Senders > Local Good Sender IPs).

The Message Audit Log indicates that the message has been rejected by the msg_reject_other event.

vm-sbg> malquery -p 10m -e "IRCPTACTION*msg_reject"
<malResults count="1">
        <message UID="0aa0f847-b7f2a8e000005526-5c-51f2f8d9b5c3">
                <events>
                        <event time="1374877913" name="ACCEPT">192.0.2.70:60434</event>
                        <event time="1374877913" name="IRCPTACTION">&lt;none&gt;|msg_reject_other</event>
                </events>
        </message>
        <avg_events_per_email>2</avg_events_per_email>
</malResults>

 450 4.3.2 try again later

Whitelisting an IP address exempts it from anti-spam scanning. However, the IP address is still subject to Directory Harvest Attack (DHA) and Email Virus Attack (EVA) policies, if those policies are enabled.