The best way to troubleshoot this is to run the Stratagy trace. Choose SMTPSEND_New Message as the template and the user you're testing with. Pick the color red as the text so that it stands out in the trace log. Then leave a message for the user and look at the trace which is in real time. The general steps the iES does when it tries to send out is that it does an NSLOOKUP to find the SMTP server. It needs a valid DNS server to do this as Ed pointed out above. You will see that in the trace if it fails to resolve the domain. However, it skips this step if in the Stratagy parameters has the sys_smtpserver_gateway defined. If that field is defined, make sure it's valid. If it gets as far as contacting the SMTP server, you will see the response from server. Another common problem is that the customer's IP is blacklisted. If so, you will see that in the trace.