Hi Andrey,
Thanks for reaching out. The variable Octopus.Deployment.SpecificMachines will only be populated with machines if prior to start your deployment, you select a specific list of targets as shown on the attached screenshot, instead of just deploying to everything on the target environment.
If you want to list the machines on the deployment on an email, there’s not a variable for that, but there is a rather cumbersome way to do it. My pal Michael did a very good job explaining it on the link below
Best regards,
Dalmiro
