disabling postfix "Undelivered Mail Returned to Sender"

Is it possible to disable the postfix notification "Undelivered Mail Returned to Sender"?

Since I receive too much spam with forged senders, I don't want postfix to notify these forged senders.

If you make postfix just reject the mail as it comes in, it doesn't use the sender address, it just refuses the email at the "RCPT TO" stage. Make sure you have

soft_bounce=no
unknown_local_recipient_reject_code = 550

I'm not sure what else you've got going on, but at least on my postfix, if somebody attempts to send an email to an unknown local user, it gets bounced early in the connection rather than after they've connected and sent you the message.

The question is why your MTA accepts mails to non-existent recipients in the first place. It should just finish the SMTP dialog with the connecting (Spam-) client with a permanent error (5xx) message. You should really have a good reason disabling DSNs (delivery status notifications).

See smtpd_recipient_restrictions or more precisely the restriction reject_unverified_recipient in the Postfix manual. You should also read the Postfix Address Verification Howto.