This doesn't use any email functionality because I don't have that available to test but I was able to create a basic app using the Incoming Webhooks function when building an app in Slack.
Slack will provide an example using Curl that can be used in a script on the Smartevent server.
In my case, my script is placed under /home/admin/scripts
#!/bin/bash
curl_cli -kX POST -H 'Content-type: application/json' --data '{"text":"Hello, World!"}' https://hooks.slack.com/services/RANDOMSTRINGPROVIDEDBYSLACK
I then created an automatic reaction that triggers the script when called.
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When triggered, it runs the curl script to post whatever message is defined in the "--data" portion of the curl command.
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I'm sure there are better options available when interacting in Slack, but this was my quick effort that might provide some direction.