TeamCity build configuration not using private docker feed

Hi,

I try to run a docker build on my TeamCity server. I configured a private docker feed to store the images which are built. This is the configuration I use:

import jetbrains.buildServer.configs.kotlin.v2019_2.*
import jetbrains.buildServer.configs.kotlin.v2019_2.buildFeatures.dockerSupport
import jetbrains.buildServer.configs.kotlin.v2019_2.buildSteps.PowerShellStep
import jetbrains.buildServer.configs.kotlin.v2019_2.buildSteps.dockerCommand
import jetbrains.buildServer.configs.kotlin.v2019_2.buildSteps.powerShell
import jetbrains.buildServer.configs.kotlin.v2019_2.triggers.vcs

version = "2020.2"

project {

    buildType(Build)
}

object Build : BuildType({
    name = "Build"

    buildNumberPattern = "%Major%.%Minor%.%Fix%.%build.counter%"

    params {
        param("Fix", "0")
        param("Major", "1")
        param("Minor", "0")
    }

    vcs {
        root(DslContext.settingsRoot)

        cleanCheckout = true
    }

    steps {
        
        dockerCommand {
            name = "Build Frontend"
            commandType = build {
                source = file {
                    path = "src/Frontend/Dockerfile"
                }
                contextDir = "src"
                namesAndTags = "dummy.frontend:%build.number%"
                commandArgs = "--pull"
            }
        }
        dockerCommand {
            name = "Push Frontend"
            commandType = push {
                namesAndTags = "dummy.frontend:%build.number%"
                removeImageAfterPush = false
            }
        }
    }
    triggers {
        vcs {
        }
    }

    features {
        dockerSupport {
            loginToRegistry = on {
                dockerRegistryId = "PROJECT_EXT_2"
            }
        }
    }
})         

Unfortunately, the build is not using the private feed. I set up the feed under the project settings connections and the test there is successful. I also added the build feature. The log is as following:

22:40:46  in directory: D:\TeamCity_Agents\BuildAgent3\work\4d7663e8d4e3f6c9

I don't know why it always tries to push to docker.io as I NEVER want to use it to push to. 

Why is the configuration not using the private docker feed? Can I prevent the build from using docker.io in general (blacklist it)?

Best regards