It's in the troubleshooting guide for Cisco Unity Connection Transcription / SpeechView, so this post basically serves as an easy to find note-to-self.
You can generate an email from Unity Connection to any address you'd like using the SpeechView stt-service alias to test SMTP routing from the CLI. The command is:
run cuc smtptest email@example.com
The recipient should recieve a test email from the Unity Connection server, and a simple successful reply will be recieved and noted via CLI as well. This test appears to only be available if SpeechView has been configured, but also served nicely as a test where an administrator was having issues configuring Accept and Relay appropriately under Message Actions.