We have a Windows 2012 web server which has recently been having a few problems with sending the odd SMTP email (generated by an ASP web application). I don't know much about this but I've been tasked with trying to sort it. When either of the errors below occur, the email in question sits on the server in the SMTP queue folder. The only solution until now has been to remote in to the server and manually delete the offending email. In the Event log we see the following -
Message delivery to the host '<destination IP' failed while delivering to the remote domain 'customer.co.uk' for the following reason: An SMTP protocol error occurred.
The SMTP verb which caused the error is 'HELO'. The response from the remote server is '501 Syntax error in parameters or arguments
Message delivery to the host 'Our external IP' failed while delivering to the remote domain 'ourcompanyname.com' for the following reason: The connection was dropped by the remote host.
Can anyone offer assistance?