When the issue occurs again a Windows Event Log entry is created from source "Symantec Mail Security for Microsoft Exchange" with ID 398:
Symantec Mail Security for Microsoft Exchange cannot verify the SMTP address of sender <X400 email address>. Content filtering will be skipped for these senders until this sender can be resolved in Active Directory
LDAP Query: <query>
LDAP Source: <IP/Hostname of LDAP server used>
Perfmon can also be used to determine if there are delays contacting the LDAP source. Collect the perfmon counter MSExchangeDSAccess Processes\LDAP Search Time counter as per this Microsoft Technet article to determine if LDAP search times are the source of the problem.
Imported Document ID: TECH134342
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