1. I have a query that if i want to avoid duplicate mails in pst.So is there any way to filter or avoid duplicate mails.
2.how to add attachment to the mail.
Thank you for writing to us.
I am afraid there is no way to avoid duplicate mails in a pst, as upon each message addition, a new EntryID is assigned to the message.
For adding messages to a mail, you can refer to:
How to Add and save attachments using MailMessage
Managing attachments with Outlook using MapiMessage
Please let us know if we can be of any of any additional help to you in this regard.