In API Gateway | Administration | Destinations | Email configuration I define the various settings.
Pressing the Test button results in:

I’ve tested with and without defining various email fields, but always populating the test email (required).
There is a single error message in the server log:
[ISC.0077.0004E] Exception during pub.client:smtp, type: javax.mail.MessagingException, msg: Could not connect to SMTP host: xyz.nowhere.com, port: 25
(hostname in the error string above is phony for this post)
At the command-line on the server hosting gateway, here are all the results of trying to figure out why the error occurs:
ping - successful
traceroute - shows the right route
telnet 25 - successful
curl - email successfully sends
Based upon this, it does not appear to be a network issue (firewalls, intrusion prevention, etc.) between the IS/GW host and the SMTP server.
Even more interesting, running pub.client:smtp directly on the IS instance hosting the GW works fine. The GW uses this service to send the email per the bolded text above.
The SMTP server is internal. It is an open relay. No username/pw needed to send mail.
It would appear that GW is doing something unexpected or requires something that I haven’t specified in the configuration when sending a test email. Any ideas from anyone are welcome.
Rob
#API-Gateway#webMethods