I have a workflow that files scanned documents in certain folders based upon the templates and metadata fields.  It also has an e-mail task that sends a copy of the scanned documents to certain e-mail addresses.  The workflow works as expected for filing, but the e-mail task stopped sending e-mails sometime after 8/23/18.   The workflow does not error, but the e-mails never arrive.

The e-mail task uses the default e-mail server and sender defined in the "Workflow Administration Console".    That e-mail server is set to use SMTP with an Exchange server and it is done anonymously.  This was working, but sometime after 8/23/18 (the last day an e-mail arrived) it stopped working.  The logging on the exchange server doesn't even show an attempted connection from that machine.  That "Workflow Administration console"->"External Objects"->Email can send a test message with no problem.

I rebooted the server, but that didn't make a difference.  I also tried adding a new e-mail server entry name (other than the default one), but that didn't work either in the task (but the console could send a test e-mail message).

What could be wrong, since nothing has changed either with the Workflow server or the Exchange Server?