Me said:
To avoid/prevent future emails
Um, think for a second. You already blocked them so you won't see
future e-mails from them. If you define a server-side rule, you won't
even have to bother downloading them to your e-mail client since they
will get deleted up on the mail server.
Just how is an alert from you going to force the sender to stop sending
you their e-mails?
If this regards spam, you really think the spammer is using a valid
e-mail address or their own e-mail address? How long have you been
using e-mail?
You trying to punish a spammer with fake bounces only makes you look
foolish. Since they don't use their own e-mail address, you will be
sending your fake bounce to an innocent. This is called backscatter and
it can be reported as spam to blacklists, so you could get yourself
blacklisted for deliberately misdirected your fake bounces at innocents.
