We have Exchange 2003 and we could send/receive emails outside our domain without problems.
Yesterday we had problems with our internet link, and our ISP fixed it, but after that we can receive emails from outside/inside network and only send internally, but not to outside domains (outlook.com, gmail.com etc).
Here’s the smtp log:
This is an SMTP protocol error log for virtual server ID 1, connection #8.
The remote host “xx.xx.xx.xx”, responded to the SMTP command “rcpt” with “550-Please turn on SMTP Authentication in your mail client.
550-ser.bpro.xxxxxxx-xxx.bih.net.ba (our_domain.org) [xxx.xx.xx.xx]:5666 is 550 not permitted to relay through this server without authentication. “.
The full command sent was “RCPT TO: “. This will probably cause the connection to fail.
A non-delivery report with a status code of 5.5.0 was generated for recipient rfc822; [email protected] (Message-ID ).
Cause: This message indicates a generic protocol error (SMTP error). For example, the remote SMTP responds to an issued EHLO with a 500 level error and the sending system will QUIT the connection and report this with NDR indicating the remote SMTP server canÆt handle the protocol.
Solution: View the SMTP log or run a netmon trace to see why the remote SMTP server rejects the protocol request.