Exception when sending mail to client on a different mail server

Question

Hi,
When i try to send a mail to a client on a different mail server from mine I am getting the following exception.
javax.mail.SendFailedException: Sending failed;
nested exception is:
     class javax.mail.SendFailedException: Invalid Addresses;
nested exception is:
     class javax.mail.SendFailedException: 550 not local host yahoo.com, not a gateway
It works perfectly fine when i send a mail to a client on my mail server. I am stuck up at this point - PLEASE HELP, any help greatly appreciated.
Thank you,
npaila

Answer 1

Most of these are, of course, anti-Spam measures implemented by the various SMTP hosts, to prevent spammers from using their servers to spread the stuff (what you're doing is exactly what Spammers do as well).
In general, most properly configured SMTP servers will only accept messages if:
(a) Your IP address (as seen by that SMTP server) maps back to a proper host name, AND
(b) The recipient of the message is "local" as determined by that SMTP server, AND
(c) In many cases, the SMTP server will also cross-check your HELO/EHLO address and the MAIL FROM: value.
It may take a few attempts to get all this right.