Thanks, Terry,
Unfortunately, this isn't a network security issue. Cold Fusion (the server, not the language) used to allow you to specify a server in the CFMAIL tag and, if that server was designated in the administrator, then it would use the credentials setup there to send the message.
Lucee also allows you to specify a server in the CFMAIL tag but does not cross-reference to see if that server is already setup in the administrator. Consequently, if you want to use different SMTP servers and those SMTP servers require authentication, then using the server attribute means you have to specify the username and password in the CFMAIL tag, too. Otherwise, you get the "530 Authentication required" response back from the SMTP server.
Since my preference would to not hardcode credentials, an enhancement request would be for Lucee to check to see if the SMTP server designated in the CFMAIL tag attribute is configured in the administrator prior to queueing the message and, if so, using the administrator credentials for SMTP authentication. I suppose a workaround would be to load the credentials through a variable instead.
Thanks again.