If you don't care about mail spoofing set (and if it is allowed) then set your sender to MAILER-DAEMON@yourdomain.com and send something like this back (or just send using your address, depending of how technically versed the intended recipient is)
This is the mail system at host mail.domain.com.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can
delete your own text from the attached returned message.
The mail system
<your.address@domain.com>: unknown user: "your.address"
Reporting-MTA: dns; your.mail.server
X-Postfix-Queue-ID: 7C5A8244352
X-Postfix-Sender: rfc822; root@your.mail.server
Arrival-Date: Sat, 25 Jan 2014 15:23:22 +0100 (CET)
Final-Recipient: rfc822; your.address@mail-server.com
Action: failed
Status: 5.1.1
Diagnostic-Code: X-Postfix; unknown user: "your.name"
That should be more or less clear (and frightening).
Note that if the receiving party is a little smart they will find out that this is a scam ;-)
Oh, and don't send anything back to spammers. Just make them believe you're dead.
since he said gmail, this is off topic – Keltari – 2016-07-10T07:12:25.197
@Aeronuts you could use https://blocksender.io/ to create bounce back messages for specific senders.
– user797717 – 2019-02-02T21:45:01.643What email services are you using? gmail? yahoo? or something else? – cybernard – 2014-01-26T03:42:52.393
cybernard, I'm using gmail. – Aeronuts – 2014-01-27T04:52:11.647