question

Ok, I think I see what you are doing. Give this a try. Note that I did not have a way to test this. There may be errors in the code.

  Param(
      $MailList = ""
  )    
        
  foreach ($Module in $Modules)
  {
      if (-not(get-module $module))
      {
          Import-Module $Module -ErrorAction Stop
      }
  }
        
  $SyncStatusNotMatch = @(
      "Enabled"
      "Success"
  ) -join "|"
        
  $CSVPath = "\\winrepo\winscripts\Get-SyncStatusAlert\SyncStatus.csv"
        
  If (-not(test-path $CSVPath))
  {
      Write-Verbose "$(Get-Date): CSV does not exist it is being created" -Verbose
      $Null = New-Item $CSVPath -ErrorAction Stop
  }
        
  Write-Verbose "$(Get-Date): Importing CSV for previous alerts" -Verbose
  if ($env:Winusername)
  {
      Write-verbose "$(Get-date): Creating Secret Server Login" -Verbose
      $SecurePassword = ConvertTo-SecureString $env:WinPassword -AsPlainText -Force -ErrorAction Stop
      $SSCred = New-Object System.Management.Automation.PSCredential ($env:WinUserName,$SecurePassword) -ErrorAction Stop
      $null = Get-SecretServerToken -OperatorCredentials $SSCred -ErrorAction Stop
  }
  $SyncStatus = Import-Csv $CSVPath -ErrorAction Stop
        
  Write-Verbose "$(Get-Date): Obtaining data from Netscalers" -Verbose
  $NSexsre = Get-sre
        
  Write-Verbose "$(Get-Date): Comparing existing alerts with new alerts" -Verbose
  $StillActives = foreach ($Status in $SyncStatus)
  {
      $StatusResult = $nsexsre |
          Where-Object hasyncstatus -notmatch $SyncStatusNotMatch |
          Where-Object hasyncstatus -eq $Status.hasyncstatus |
          Where-Object name -eq $Status.name
        
      if ($Null -ne $StatusResult)
      {
          [pscustomobject]@{
              Name         = $Status.name
              HAState      = $Status.HAState
              HASyncStatus = $Status.HASyncStatus
              AlertDate    = $Status.AlertDate
              EmailSent    = $False 
          }
      }
  }
        
  $SendAlert = @()
        
  if ($StillActives.count -gt 0)
  {
      Write-Verbose "$(Get-Date): Verifying if a previous alert has not been sent in 12 hours" -Verbose
      foreach ($StillActive in $StillActives)
      {
          $SAtimespan = New-TimeSpan –Start $StillActive.Alertdate –End (get-date)
          If (($SAtimespan.TotalMinutes -gt 10) -and ($StillActive.emailsent = $false))
          {                                                      # This entry has been seen for at least 10 minutes 
              $StillActive.emailsent = $True                     # no need to send another email alert for 12 hours 
              $SendAlert += $StillActive                         # send an email
          }
          if ($SAtimespan.TotalMinutes -gt (12 * 60))
          {                                                      # This entry has been down for a long time,   
                StillActive.EmailSent = $false                     # Include in the alert email once every 12 hours 
              StillActive.AlertDate = (get-date)                 # start the 10 minute clock ticking again.  
          }
      }
        
      $nsexsrefiltered = ($NSExsre |
          Where-Object hasyncstatus -NotMatch $SyncStatusNotMatch |
          Where-Object name -notmatch ($StillActives.name -join "|")
      )
  }
  else
  {
      $nsexsrefiltered = $NSExsre | Where-Object hasyncstatus -NotMatch $SyncStatusNotMatch
  }
     
 # Now we can update the CSV
    
  if ($Null -ne $nsexsrefiltered)
  {
      Write-Verbose "$(Get-Date): Adding new alerts to the list" -Verbose
      $UpdateList = foreach ($ns in $nsexsrefiltered)
      {
          [pscustomobject]@{
              Name         = $ns.Name
              HAState      = $ns.HAState
              HASyncStatus = $ns.HASyncStatus
              AlertDate    = (Get-Date)
              EmailSent    = $False 
          }
      }
  }
        
  if(($Null -eq $StillActives) -and ($null -eq $UpdateList))
  {
      $NoAlerts =
      [pscustomobject]@{
          Name         = $Null
          HAState      = $Null
          HASyncStatus = $Null
          AlertDate    = $Null
          EmailSent    = $Null
      }
      $NoAlerts | Export-Csv $CSVPath -NoTypeInformation
  }
  Else
  {
      if ($Null -ne $UpdateList)
      {
          $ActivesToExport = $StillActives + $UpdateList
          $ActivesToExport | Export-Csv $CSVPath -NoTypeInformation
      }
      else
      {
          $StillActives | Export-Csv $CSVPath -NoTypeInformation
      }
  }
     
    
 # Send out the alert email. 
     
  # UpdateList contains new alerts, but we can't do anything with them until 10 minutes have passed.  
  #If ($Null -ne $UpdateList)
  #{
  #   $SendAlert += $UpdateList
  #}
        
  If ($SendAlert.count -ne 0)
  {
      Write-Verbose "$(Get-Date): Sending email to $MailList" -Verbose
      Foreach ($Alert in $SendAlert)
      {
          Write-Verbose "$(Get-Date): Sending Alert for: $($Alert.name)" -Verbose
      }
        
      $Style = @"
          <style>
          BODY{font-family: Arial; font-size: 10pt;}
          TABLE{border: 1px solid black; border-collapse: collapse;}
          TH{border: 1px solid black; background: #dddddd; padding: 5px; }
          TD{border: 1px solid black; padding: 5px; }
          .odd {background: #DCDCDC;}
          .even {background: #FFFFFF;}
        
          </style>
 "@
        
      $PreContent = "Link to the SOP for addressing this issue: https://x/vAMsFQ"
      $Message = $SendAlert | ConvertTo-Html -Head $style -PreContent $PreContent | Set-AlternatingRows -CSSEvenClass even -CSSOddClass odd
      $MailSplat = @{
          To         = $MailList
          From       = "noreply@.com"
          SmtpServer = "hub.corp.com"
          Subject    = "out of Sync"
          Body       = $Message | Out-String
          BodyAsHtml = $true
      }
        
      Send-MailMessage @MailSplat
  }
  Else
  {
      Write-Verbose "$(Get-Date): No Alerts to send" -Verbose
  }

Thanks @MotoX80 that was much helpful, I was wondering if we can do this instead, which will not send an alert if it is send already in the last 12 hrs + it exists for 10 mins in a single line. Thoughts?

foreach ($StillActive in $StillActives)
{
$SAtimespan = New-TimeSpan –Start $StillActive.Alertdate –End (get-date)
if ((Get-Date ($StillActive.alertdate)) -lt ((get-date).AddHours(-12)) -and ($SAtimespan.TotalMinutes -gt 10))
{
$SendAlert += $StillActive
}
}

This should send the alert out after 12 hours, without waiting the extra 10 minutes as I initially had it.

      foreach ($StillActive in $StillActives)
       {
           $ForceAlert = $False
           $SAtimespan = New-TimeSpan –Start $StillActive.Alertdate –End (get-date)
           if ($SAtimespan.TotalMinutes -gt (12 * 60))
           {                                                      # This entry has been down for a long time,   
               StillActive.EmailSent = $false                     # Include in the alert email once every 12 hours 
               StillActive.AlertDate = (get-date)                 # Reset the time so we don't send another alert for 12 more hours 
               $ForceAlert = $True   
           }
           If ((($SAtimespan.TotalMinutes -gt 10) -and ($StillActive.emailsent = $false)) -or ($ForceAlert))
           {                                                      # This entry has been seen for at least 10 minutes 
               $StillActive.emailsent = $True                     # no need to send another email alert for 12 hours 
               $SendAlert += $StillActive                         # send an email
           }
       }