I haven't used the email functionality in the ecom*
however...
SMTP 550 shows as a "relay" related error.
From reading your other posts, it looks like you tried using smtpout.secureserver.net (which is godaddy I think) and you reported success. Now you are trying to use a smtp server inside your LAN?
My guess is that the server wants you to authenticate before it will send on your messages. Therefore, you need to either change the client or the server. A quick glance at Netedit makes me think that is not possible to have the ecom authenticate, I dont even see a place for a username\password. Therefore can you
configure the email server to allow non authenticated clients either globally (bad idea because of spam I think.), maybe
by IP address or somehow.
links:
http://en.wikipedia.org/wiki/Open_mail_relayhttp://social.technet.microsoft.com/Forums/en-US/exchangesvrtransport/thread/1a84a06a-f1c8-40b4-ace8-1e264f218aa1/