..the contributors to this usenet discussion group as though
they were a help desk?  It seems so, because..

If you had read this groups for a couple of days before
posting, you might have read a very recent discussion
on that very subject, and if you were to actually *search*
the archive of this group at Google Groups (God forbid!)
using the terms 'bounce' and 'mail', then sort those posts
by date, it will be right near the top.

If you cannot be bothered reading the group, GIYF

Can you help yourself?

From a recent posting on the same subject....

Subject: Re: java mail handling bounced messages
From: "Greg R. Broderick" <usenet200707@blackholio.dyndns.org>
Newsgroups: comp.lang.java.programmer

ameyas7 <amey.samant@gmail.com> wrote in news:1186065498.319240.38510
@d30g2000prg.googlegroups.com:

A sent mail may 'bounce' in one of two ways:

1.  the SMTP server to which you (the mail user agent/mail client) are
sending the mail may reject the message either temporarily or permanently.
This is handled with an SMTP result code of 4xx (temporary failure) or
5xx (permanent failure), where the precise reasoning for the failure can
be determined from the other two digits of the result code.  Consult RFC
2821 for the gory technical details of SMTP response codes.  You may
detect and trap these in the sending SMTP client software immediately when
the message is sent -- this provides a synchronous feedback when the
message is immediately rejected.

2.  SMTP and the Internet mail architecture is, by design,
store-and-forward -- you send a message to an intermediate host (your
ISP's mail server) which stores the message and forwards it on to another
intermediate host, until it eventually reaches the recipient.  This
storage and forwarding happens after the initial sending of the message
from the mail client to the mail server has completed successfully, thus
no synchronous means is available to notify the mail client that the
message has been rejected or bounced by one of the intermediate hosts.
What most mail servers will do is to return an email message to the
putative sender's email box, containing an error message, indicating why
the message failed to be sent, and possibly the original message.  This
message may be retrieved from the sender's email box using whatever method
(usually POP3 or IMAP) the mail client normally uses to retrieve inbound
email messages.

Due to the nature of SMTP as a store-and-forward mail system, this can not
happen synchronously, thus no synchronous feedback is possible when one of
the intermediate hosts further down the line rejects the sender's email.

For more information, please consult the various Internet RFCs concerning
email and SMTP.

Cheers!
GRB