|First, keep in mind that BlueDragon spools mail to a work/cfmail/spool directory in the [BlueDragon-install] directory for Server and Server JX, or in the WEB-INF of a deployed web application in BlueDragon for J2EE. The work directory for the .NET edition will depend on your installation choice, so see the manual, "Deploying CFML on ASP.NET Servers" for more information.
The work/cfmail directory also holds a mail.log which reports information about the mailing process (starting the mailserver process) as well as failures to send email.
As in CF, all undeliverable messages are filed away for your review. In BlueDragon, they're held in the work/cfmail/undelivered folder (each with a filename comprised of a long string of characters and numbers and an extension of .email.)
A common failure would be if the SMTP server used for the CFMAIL could not be reached. That will be logged for each failed message. As for the SMTP server, you can either specify a mail server in the SERVER attribute of CFMAIL or BlueDragon will default to that specified in the BlueDragon Administrator.
If the mail server was just down at the time of the emailing, you could copy the files from the undelivered to the spool directory to have BlueDragon attempt to send them again.
Yet another common problem is if the mail server requires a username and password. This too will cause delivery failures which will be logged for each failed message (though it may report a timeout rather than a specific authentication failure). You can provide this on the CFMAIL tag or in the admin console. Note that you specify it in the admin console by prefacing the name of the mail server (or IP address) with username:password@ (as in, for instance, myname:firstname.lastname@example.org).
Finally, another common problem is that some mail servers fail to accept mail if the FROM address is different than the domain of the mail server sending the message (called "open relay"). Again, view the cfmail log file to determine if this is a problem.