Hi @mrthanhkhoi 

Attaching files to email notifications using Business Events is currently not natively supported in Acumatica as of my knowledge.

However, you may consider a workaround using Acumatica's customization capabilities:

1. Customize Email Sending Mechanism: You can customize the email sending mechanism to include attached files from the corresponding sales order record. This would likely involve modifying the graph that sends the emails, to fetch the files attached to the Sales Order and include them in the outgoing email.

   public class SOOrderEntry_Extension : PXGraphExtension<SOOrderEntry>
   {
       // Event Handler for the 'SendEmail' button
       public delegate void SendEmailDelegate(PXCache cache, PX.SM.Email email);
        PXOverride]
       public void SendEmail(PXCache cache, PX.SM.Email email, SendEmailDelegate baseMethod)
       {
           // Invoke the original method
           baseMethod?.Invoke(cache, email);
   
           // Get the current SOOrder record
           var soOrder = Base.Document.Current;
   
           if (soOrder != null)
           {
               // Get all files attached to the SOOrder
               foreach (PX.SM.UploadFile file in PXNoteAttribute.GetFileNotes(Base.Document.Cache, soOrder))
               {
                   // Attach each file to the email
                   PX.SM.UploadFileInq.AddFile(email, file);
               }
           }
       }
   }
   

   Please note that the above code is not a ready-to-use solution, but rather an illustration of the approach you can take. You might need to adapt it to your specific needs.

2. Use of Third-Party Tools: You could potentially employ third-party tools like Postman or Zapier to access Acumatica's REST API for gathering attachment files and sending the email.

3. In either case, given that this is not a standard feature of Acumatica, you might want to reach out to Acumatica support or to an Acumatica customization consultant to assist with this.