I am using TeamCity to deploy packages to Octopus, and in TC i can see list of changes, done by our developers in curent deployment. So the question is it possible somehow to get this list of changes in Octopus and than add it into Email notification step.
Check out the documentation on Octopus' own site... it even provides a sample template that includes the Release Notes in the email step
You can then hook up TeamCity to push changes to the Release Notes within Octopus. This can be achieved via the Octopus REST API: https://octopus.com/docs/api-and-integration/teamcity