TI map Email entity to SecurityEvent

Original query, unchanged.

let dt_lookBack = 1h;
let ioc_lookBack = 14d;
let emailregex = @'^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$';
ThreatIntelligenceIndicator
//Filtering the table for Email related IOCs
| where isnotempty(EmailSenderAddress)
| where TimeGenerated >= ago(ioc_lookBack)
| summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by IndicatorId
| where Active == true and ExpirationDateTime > now()
// using innerunique to keep perf fast and result set low, we only need one match to indicate potential malicious activity that needs to be investigated
| join kind=innerunique (
(union isfuzzy=true
(SecurityEvent
| where TimeGenerated >= ago(dt_lookBack) and isnotempty(TargetUserName)
//Normalizing the column to lower case for exact match with EmailSenderAddress column
| extend TargetUserName = tolower(TargetUserName)
// renaming timestamp column so it is clear the log this came from SecurityEvent table
| extend SecurityEvent_TimeGenerated = TimeGenerated
),
(WindowsEvent
| where TimeGenerated >= ago(dt_lookBack)
| extend TargetUserName = tostring(EventData.TargetUserName)
| where isnotempty(TargetUserName)
//Normalizing the column to lower case for exact match with EmailSenderAddress column
| extend TargetUserName = tolower(TargetUserName)
// renaming timestamp column so it is clear the log this came from SecurityEvent table
| extend SecurityEvent_TimeGenerated = TimeGenerated
))
)
on $left.EmailSenderAddress == $right.TargetUserName
| where SecurityEvent_TimeGenerated < ExpirationDateTime
| summarize SecurityEvent_TimeGenerated = arg_max(SecurityEvent_TimeGenerated, *) by IndicatorId, TargetUserName
| project SecurityEvent_TimeGenerated, Description, ActivityGroupNames, IndicatorId, ThreatType, Url, ExpirationDateTime, ConfidenceScore,
EmailSenderName, EmailRecipient, EmailSourceDomain, EmailSourceIpAddress, EmailSubject, FileHashValue, FileHashType, Computer, EventID, TargetUserName, Activity, IpAddress, AccountType,
LogonTypeName, LogonProcessName, Status, SubStatus
| extend HostName = tostring(split(Computer, '.', 0)[0]), DnsDomain = tostring(strcat_array(array_slice(split(Computer, '.'), 1, -1), '.'))
| extend timestamp = SecurityEvent_TimeGenerated