Check out this post on Blog by Florian Courgey, by our own Community MVP @Florian_Courgey, about sending Message Center real-time emails from workflows using JavaScript . This post explains how from a workflow in Classic instance A, you can send a SOAP message to Message Center instance B.
Blog Post URL: Send Message Center realtime emails from Workflows! (Javascript)
In case of queries, feel free to reach out through the below comment section.
