I have a Domino development server I can't get web-based emails to send from. The error I'm getting is "The remote server is not a known TCP/IP host". The server works fine for Notes based emails, but I'm generating emails from LotusScript in an app, and they are not sending. This server was recently created (Dom 8.5.3).
I have the server sending email directly to the Internet on all location documents (for Notes client).
See IBM Technote #1099632 "Notes/Domino background agent fails to send mail; Errors may occur in logs":
The Technote also provides steps to troubleshoot the issue.
Also, you can enable some debugging to determine where the problem surfaces.
See Collecting data for Domino SMTP mail routing issues for more details on that