Exchange workflow MailItemsAccessed operation anomaly

Original query, unchanged.

let starttime = 14d;
let endtime = 1d;
let timeframe = 1h;
let scorethreshold = 1.5;
let percentthreshold = 50;
// Preparing the time series data aggregated hourly count of MailItemsAccessd Operation in the form of multi-value array to use with time series anomaly function.
let TimeSeriesData =
OfficeActivity
| where TimeGenerated  between (startofday(ago(starttime))..startofday(ago(endtime)))
| where OfficeWorkload=~ "Exchange" and Operation =~ "MailItemsAccessed" and ResultStatus =~ "Succeeded"
| project TimeGenerated, Operation, MailboxOwnerUPN
| make-series Total=count() on TimeGenerated from startofday(ago(starttime)) to startofday(ago(endtime)) step timeframe;
let TimeSeriesAlerts = TimeSeriesData
| extend (anomalies, score, baseline) = series_decompose_anomalies(Total, scorethreshold, -1, 'linefit')
| mv-expand Total to typeof(double), TimeGenerated to typeof(datetime), anomalies to typeof(double), score to typeof(double), baseline to typeof(long)
| where anomalies > 0
| project TimeGenerated, Total, baseline, anomalies, score;
// Joining the flagged outlier from the previous step with the original dataset to present contextual information
// during the anomalyhour to analysts to conduct investigation or informed decisions.
TimeSeriesAlerts | where TimeGenerated > ago(2d)
// Join against base logs since specified timeframe to retrive records associated with the hour of anomoly
| join kind=innerunique (
    OfficeActivity
    | where TimeGenerated > ago(2d)
    | extend DateHour = bin(TimeGenerated, 1h)
    | where OfficeWorkload=~ "Exchange" and Operation =~ "MailItemsAccessed" and ResultStatus =~ "Succeeded"
    | summarize HourlyCount=count(), TimeGeneratedMax = arg_max(TimeGenerated, *), IPAdressList = make_set(Client_IPAddress, 1000), SourceIPMax= arg_max(Client_IPAddress, *), ClientInfoStringList= make_set(ClientInfoString, 1000) by MailboxOwnerUPN, Logon_Type, TenantId, UserType, TimeGenerated = bin(TimeGenerated, 1h)
    | where HourlyCount > 25 // Only considering operations with more than 25 hourly count to reduce False Positivies
    | order by HourlyCount desc
) on TimeGenerated
| extend PercentofTotal = round(HourlyCount/Total, 2) * 100
| where PercentofTotal > percentthreshold // Filter Users with count of less than 5 percent of TotalEvents per Hour to remove FPs/ users with very low count of MailItemsAccessed events
| order by PercentofTotal desc
| project-reorder TimeGeneratedMax, Type, OfficeWorkload, Operation, UserId, SourceIPMax, IPAdressList, ClientInfoStringList, HourlyCount, PercentofTotal, Total, baseline, score, anomalies
| extend AccountName = tostring(split(UserId, "@")[0]), AccountUPNSuffix = tostring(split(UserId, "@")[1])