first shot at building postfix container

.gitea/workflows/container.yml

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+name: Build OCI Containers
+on:
+  push:
+
+jobs:
+  build-container:
+    name: Build Containers
+    runs-on: ubuntu-latest
+    container:
+      image: catthehacker/ubuntu:act-latest
+    env:
+      DOCKER_HOST: tcp://docker:2376
+      DOCKER_CERT_PATH: /certs/client
+      DOCKER_TLS_VERIFY: 1
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Setup Docker Certs
+        run: |-
+          mkdir -p /certs/client
+          echo "${{ secrets.DOCKER_CERT }}" > /certs/client/cert.pem
+          echo "${{ secrets.DOCKER_KEY }}" > /certs/client/key.pem
+          echo "${{ secrets.DOCKER_CA }}" > /certs/client/ca.pem
+
+      - name: Login to Gitea registry
+        uses: docker/login-action@v2
+        with:
+          registry: git.domainforge.de
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.REGISTRY_TOKEN }}
+
+      - name: Build and push Postfix Container
+        uses: docker/build-push-action@v2
+        with:
+          context: postfix
+          file: Dockerfile
+          push: true
+          tags: git.domainforge.de/public/postfix:latest

postfix/Dockerfile

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+FROM debian:bookworm-slim
+
+RUN apt-get update && \
+    apt-get -y upgrade && \
+    apt-get -y --purge autoremove && \
+    apt-get -y install postfix && \
+    apt-get -y clean
+
+EXPOSE 25/tcp
+EXPOSE 465/tcp
+EXPOSE 587/tcp
+
+CMD ["/usr/sbin/postfix", "start-fg"]