Macro to send email when a resource is assigned

I want to create a Macro in MS Project that will send an outlook email when a resource is assigned. My issue is that I want it to only notify the resources that have been assigned since the last time the macro was run because i don't want everyone getting duplicate emails every time.

Currently my code successfully emails every assignee the ask they are assigned to every time its ran. Getting it to only select newly assigned resources since the last run is where I'm stuck and don't really know where to start. Any help is appreciated!!

    Dim oProject As Project
    Dim oTask As Task
    Dim oResource As Resource
    Dim oMail As Object
    
    
    ' Get current project
    Set oProject = ActiveProject

' Loop through each task in the project
For Each oTask In oProject.Tasks

        ' Check for new assignments on this task
       If oTask.Resources.Count > 0 Then
      
            ' Loop through each resource assigned to the task
            For Each oResource In oTask.Resources
                ' Get the email address of the resource
                ' (You'll need to store email addresses in the project)
                ' Use the resource's email address to create the email
                Set oMail = CreateObject("Outlook.Application").CreateItem(0)
                With oMail
                    .To = oResource.EMailAddress
                    .Subject = "New Task Assignment"
                    .Body = "You have been assigned to task: " & oTask.Name
                    .Send  ' Or .Display
                End With
            Next oResource
        End If
    
    Next oTask

End Sub

Rather than loop through tasks, you can loop through resources, and then loop through each resource's assignments. Working at the assignment level, use a flag field to indicate whether or not this assignment has already been emailed.

For example:

Sub EmailNewAssignments()

    Dim oMail As Object
    Set oMail = CreateObject("Outlook.Application").CreateItem(0)
                
    Dim res As Resource
    For Each res In ActiveProject.Resources
    
        Dim taskList As String
        taskList = vbNullString
        
        Dim asn As Assignment
        For Each asn In res.Assignments
            If Not asn.Flag1 Then
                taskList = vbCrLf & "Task: " & asn.Task.Name
                asn.Flag1 = True
            End If
        Next asn
        
        If Len(taskList) > 0 Then
            With oMail
                .To = res.EMailAddress
                .Subject = "New Task Assignments"
                .Body = "You have been assigned to the following tasks: " & taskList
                .Send
            End With
        End If
    Next res

End Sub