Multiple users email forwarded to same destination

Original query, unchanged.

let queryfrequency = 1d;
let queryperiod = 7d;
OfficeActivity
| where TimeGenerated > ago(queryperiod)
| where OfficeWorkload =~ "Exchange"
//| where Operation in ("Set-Mailbox", "New-InboxRule", "Set-InboxRule")
| where Parameters has_any ("ForwardTo", "RedirectTo", "ForwardingSmtpAddress")
| mv-apply DynamicParameters = todynamic(Parameters) on (summarize ParsedParameters = make_bag(bag_pack(tostring(DynamicParameters.Name), DynamicParameters.Value)))
| evaluate bag_unpack(ParsedParameters, columnsConflict='replace_source')
| extend DestinationMailAddress = tolower(case(
    isnotempty(column_ifexists("ForwardTo", "")), column_ifexists("ForwardTo", ""),
    isnotempty(column_ifexists("RedirectTo", "")), column_ifexists("RedirectTo", ""),
    isnotempty(column_ifexists("ForwardingSmtpAddress", "")), trim_start(@"smtp:", column_ifexists("ForwardingSmtpAddress", "")),
    ""))
| where isnotempty(DestinationMailAddress)
| mv-expand split(DestinationMailAddress, ";")
| extend ClientIPValues = extract_all(@'\[?(::ffff:)?(?P<IPAddress>(\d+\.\d+\.\d+\.\d+)|[^\]]+)\]?([-:](?P<Port>\d+))?', dynamic(["IPAddress", "Port"]), ClientIP)[0]
| extend ClientIP = tostring(ClientIPValues[0]), Port = tostring(ClientIPValues[1])
| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), DistinctUserCount = dcount(UserId), UserId = make_set(UserId, 250), Ports = make_set(Port, 250), EventCount = count() by tostring(DestinationMailAddress), ClientIP
| where DistinctUserCount > 1 and EndTime > ago(queryfrequency)
| mv-expand UserId to typeof(string)
| extend AccountName = tostring(split(UserId, "@")[0]), AccountUPNSuffix = tostring(split(UserId, "@")[1])