diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 55595838..19a445b4 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -91,6 +91,20 @@ jobs:
         shell: bash
         run: |
           echo "BRANCH=${GITHUB_REF#refs/heads/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for branch testing
+        if: ${{ env.BRANCH == 'testing' }}
+        shell: bash
+        env:
+          COMMIT_MESSAGE: ${{ github.event.head_commit.message }}
+        run: |
+          echo "MAILU_VERSION=pr-${COMMIT_MESSAGE//[!0-9]/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for other branches than testing
+        if: ${{ env.BRANCH != 'testing' }}
+        shell: bash
+        env:
+          MAILU_BRANCH: ${{ env.BRANCH }}
+        run: |
+          echo "MAILU_VERSION=${{ env.MAILU_BRANCH }}" >> $GITHUB_ENV          
       - name: Create folder for storing images
         run: |
           sudo mkdir -p /images
@@ -124,6 +138,20 @@ jobs:
         shell: bash
         run: |
           echo "BRANCH=${GITHUB_REF#refs/heads/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for branch testing
+        if: ${{ env.BRANCH == 'testing' }}
+        shell: bash
+        env:
+          COMMIT_MESSAGE: ${{ github.event.head_commit.message }}
+        run: |
+          echo "MAILU_VERSION=pr-${COMMIT_MESSAGE//[!0-9]/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for other branches than testing
+        if: ${{ env.BRANCH != 'testing' }}
+        shell: bash
+        env:
+          MAILU_BRANCH: ${{ env.BRANCH }}
+        run: |
+          echo "MAILU_VERSION=${{ env.MAILU_BRANCH }}" >> $GITHUB_ENV          
       - name: Create folder for storing images
         run: |
           sudo mkdir -p /images
@@ -157,6 +185,20 @@ jobs:
         shell: bash
         run: |
           echo "BRANCH=${GITHUB_REF#refs/heads/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for branch testing
+        if: ${{ env.BRANCH == 'testing' }}
+        shell: bash
+        env:
+          COMMIT_MESSAGE: ${{ github.event.head_commit.message }}
+        run: |
+          echo "MAILU_VERSION=pr-${COMMIT_MESSAGE//[!0-9]/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for other branches than testing
+        if: ${{ env.BRANCH != 'testing' }}
+        shell: bash
+        env:
+          MAILU_BRANCH: ${{ env.BRANCH }}
+        run: |
+          echo "MAILU_VERSION=${{ env.MAILU_BRANCH }}" >> $GITHUB_ENV          
       - name: Create folder for storing images
         run: |
           sudo mkdir -p /images
@@ -190,6 +232,20 @@ jobs:
         shell: bash
         run: |
           echo "BRANCH=${GITHUB_REF#refs/heads/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for branch testing
+        if: ${{ env.BRANCH == 'testing' }}
+        shell: bash
+        env:
+          COMMIT_MESSAGE: ${{ github.event.head_commit.message }}
+        run: |
+          echo "MAILU_VERSION=pr-${COMMIT_MESSAGE//[!0-9]/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for other branches than testing
+        if: ${{ env.BRANCH != 'testing' }}
+        shell: bash
+        env:
+          MAILU_BRANCH: ${{ env.BRANCH }}
+        run: |
+          echo "MAILU_VERSION=${{ env.MAILU_BRANCH }}" >> $GITHUB_ENV          
       - name: Create folder for storing images
         run: |
           sudo mkdir -p /images
@@ -223,6 +279,20 @@ jobs:
         shell: bash
         run: |
           echo "BRANCH=${GITHUB_REF#refs/heads/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for branch testing
+        if: ${{ env.BRANCH == 'testing' }}
+        shell: bash
+        env:
+          COMMIT_MESSAGE: ${{ github.event.head_commit.message }}
+        run: |
+          echo "MAILU_VERSION=pr-${COMMIT_MESSAGE//[!0-9]/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for other branches than testing
+        if: ${{ env.BRANCH != 'testing' }}
+        shell: bash
+        env:
+          MAILU_BRANCH: ${{ env.BRANCH }}
+        run: |
+          echo "MAILU_VERSION=${{ env.MAILU_BRANCH }}" >> $GITHUB_ENV          
       - name: Create folder for storing images
         run: |
           sudo mkdir -p /images
@@ -256,6 +326,20 @@ jobs:
         shell: bash
         run: |
           echo "BRANCH=${GITHUB_REF#refs/heads/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for branch testing
+        if: ${{ env.BRANCH == 'testing' }}
+        shell: bash
+        env:
+          COMMIT_MESSAGE: ${{ github.event.head_commit.message }}
+        run: |
+          echo "MAILU_VERSION=pr-${COMMIT_MESSAGE//[!0-9]/}" >> $GITHUB_ENV
+      - name: Derive MAILU_VERSION for other branches than testing
+        if: ${{ env.BRANCH != 'testing' }}
+        shell: bash
+        env:
+          MAILU_BRANCH: ${{ env.BRANCH }}
+        run: |
+          echo "MAILU_VERSION=${{ env.MAILU_BRANCH }}" >> $GITHUB_ENV          
       - name: Create folder for storing images
         run: |
           sudo mkdir -p /images
diff --git a/core/admin/Dockerfile b/core/admin/Dockerfile
index 6ea12311..97cf1736 100644
--- a/core/admin/Dockerfile
+++ b/core/admin/Dockerfile
@@ -1,8 +1,8 @@
 # First stage to build assets
-ARG DISTRO=alpine:3.12
+ARG DISTRO=alpine:3.14
 ARG ARCH=""
 FROM ${ARCH}node:8 as assets
-COPY --from=balenalib/rpi-alpine:3.10 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
+COPY --from=balenalib/rpi-alpine:3.14 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
 
 COPY package.json ./
 RUN npm install
@@ -24,9 +24,9 @@ RUN mkdir -p /app
 WORKDIR /app
 
 COPY requirements-prod.txt requirements.txt
-RUN apk add --no-cache libressl curl postgresql-libs mariadb-connector-c \
+RUN apk add --no-cache openssl curl postgresql-libs mariadb-connector-c \
   && apk add --no-cache --virtual build-dep \
-  libressl-dev libffi-dev python3-dev build-base postgresql-dev mariadb-connector-c-dev cargo \
+  openssl-dev libffi-dev python3-dev build-base postgresql-dev mariadb-connector-c-dev cargo \
   && pip3 install -r requirements.txt \
   && apk del --no-cache build-dep
 
diff --git a/core/dovecot/Dockerfile b/core/dovecot/Dockerfile
index e1c20eff..22145bde 100644
--- a/core/dovecot/Dockerfile
+++ b/core/dovecot/Dockerfile
@@ -1,4 +1,4 @@
-ARG DISTRO=alpine:3.13
+ARG DISTRO=alpine:3.14
 FROM $DISTRO as builder
 WORKDIR /tmp
 RUN apk add git build-base automake autoconf libtool dovecot-dev xapian-core-dev icu-dev
diff --git a/core/nginx/Dockerfile b/core/nginx/Dockerfile
index 2bc1cfd1..1906ed31 100644
--- a/core/nginx/Dockerfile
+++ b/core/nginx/Dockerfile
@@ -1,4 +1,4 @@
-ARG DISTRO=alpine:3.12
+ARG DISTRO=alpine:3.14
 FROM $DISTRO
 # python3 shared with most images
 RUN apk add --no-cache \
diff --git a/core/none/Dockerfile b/core/none/Dockerfile
index 70041dac..51b8d1c5 100644
--- a/core/none/Dockerfile
+++ b/core/none/Dockerfile
@@ -1,6 +1,6 @@
 # This is an idle image to dynamically replace any component if disabled.
 
-ARG DISTRO=alpine:3.12
+ARG DISTRO=alpine:3.14
 FROM $DISTRO
 
 CMD sleep 1000000d
diff --git a/core/postfix/Dockerfile b/core/postfix/Dockerfile
index af29bf91..062155c1 100644
--- a/core/postfix/Dockerfile
+++ b/core/postfix/Dockerfile
@@ -1,4 +1,4 @@
-ARG DISTRO=alpine:3.12
+ARG DISTRO=alpine:3.14
 FROM $DISTRO
 # python3 shared with most images
 RUN apk add --no-cache \
@@ -12,7 +12,7 @@ RUN pip3 install socrate==0.2.0
 RUN pip3 install "podop>0.2.5"
 
 # Image specific layers under this line
-RUN apk add --no-cache postfix postfix-pcre cyrus-sasl-plain cyrus-sasl-login
+RUN apk add --no-cache postfix postfix-pcre cyrus-sasl-login
 
 COPY conf /conf
 COPY start.py /start.py
diff --git a/core/rspamd/Dockerfile b/core/rspamd/Dockerfile
index acaf074e..6706ef14 100644
--- a/core/rspamd/Dockerfile
+++ b/core/rspamd/Dockerfile
@@ -1,4 +1,4 @@
-ARG DISTRO=alpine:3.12
+ARG DISTRO=alpine:3.14
 FROM $DISTRO
 # python3 shared with most images
 RUN apk add --no-cache \
diff --git a/docs/conf.py b/docs/conf.py
index 6b19f967..8f174b64 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -4,7 +4,7 @@
 
 import os
 
-extensions = ['sphinx.ext.imgmath', 'sphinx.ext.viewcode']
+extensions = ['sphinx.ext.imgmath', 'sphinx.ext.viewcode', 'sphinx_rtd_theme']
 templates_path = ['_templates']
 source_suffix = '.rst'
 master_doc = 'index'
diff --git a/docs/requirements.txt b/docs/requirements.txt
index 4afd9bb6..f49e26d5 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -2,3 +2,4 @@ recommonmark
 Sphinx
 sphinx-autobuild
 sphinx-rtd-theme
+docutils==0.16
diff --git a/optional/clamav/Dockerfile b/optional/clamav/Dockerfile
index 1132845f..20cebcdc 100644
--- a/optional/clamav/Dockerfile
+++ b/optional/clamav/Dockerfile
@@ -1,4 +1,4 @@
-ARG DISTRO=alpine:3.12
+ARG DISTRO=alpine:3.14
 FROM $DISTRO
 # python3 shared with most images
 RUN apk add --no-cache \
diff --git a/optional/fetchmail/Dockerfile b/optional/fetchmail/Dockerfile
index a707a54a..506e409a 100644
--- a/optional/fetchmail/Dockerfile
+++ b/optional/fetchmail/Dockerfile
@@ -1,4 +1,4 @@
-ARG DISTRO=alpine:3.12
+ARG DISTRO=alpine:3.14
 FROM $DISTRO
 
 # python3 shared with most images
diff --git a/optional/postgresql/Dockerfile b/optional/postgresql/Dockerfile
index ff25a66f..0f5034da 100644
--- a/optional/postgresql/Dockerfile
+++ b/optional/postgresql/Dockerfile
@@ -1,9 +1,8 @@
-ARG DISTRO=alpine:3.12
+ARG DISTRO=alpine:3.14
 FROM $DISTRO
 # python3 shared with most images
 RUN apk add --no-cache \
     python3 py3-pip bash py3-multidict \
-  && apk add --upgrade sudo \
   && pip3 install --upgrade pip
 
 # Shared layer between nginx, dovecot, postfix, postgresql, rspamd, unbound, rainloop, roundcube
diff --git a/optional/radicale/Dockerfile b/optional/radicale/Dockerfile
index 400b1a3f..13761164 100644
--- a/optional/radicale/Dockerfile
+++ b/optional/radicale/Dockerfile
@@ -1,4 +1,4 @@
-ARG DISTRO=alpine:3.12
+ARG DISTRO=alpine:3.14
 FROM $DISTRO
 
 # python3 shared with most images
diff --git a/optional/unbound/Dockerfile b/optional/unbound/Dockerfile
index abb45420..2b472d44 100644
--- a/optional/unbound/Dockerfile
+++ b/optional/unbound/Dockerfile
@@ -1,4 +1,4 @@
-ARG DISTRO=alpine:3.12
+ARG DISTRO=alpine:3.14
 FROM $DISTRO
 # python3 shared with most images
 RUN apk add --no-cache \
diff --git a/setup/Dockerfile b/setup/Dockerfile
index 2b3c3c6c..5775ab6b 100644
--- a/setup/Dockerfile
+++ b/setup/Dockerfile
@@ -1,4 +1,4 @@
-ARG DISTRO=alpine:3.10
+ARG DISTRO=alpine:3.14
 FROM $DISTRO
 
 RUN mkdir -p /app
diff --git a/towncrier/newsfragments/1851.feature b/towncrier/newsfragments/1851.feature
new file mode 100644
index 00000000..e01f5cb4
--- /dev/null
+++ b/towncrier/newsfragments/1851.feature
@@ -0,0 +1 @@
+Remove cyrus-sasl-plain as it's not packaged by alpine anymore. SASL-login is still available and used when relaying.
diff --git a/webmails/rainloop/Dockerfile b/webmails/rainloop/Dockerfile
index 9c65f277..9814413d 100644
--- a/webmails/rainloop/Dockerfile
+++ b/webmails/rainloop/Dockerfile
@@ -3,7 +3,7 @@ ARG QEMU=other
 
 # NOTE: only add file if building for arm
 FROM ${ARCH}php:7.4-apache as build_arm
-ONBUILD COPY --from=balenalib/rpi-alpine:3.10 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
+ONBUILD COPY --from=balenalib/rpi-alpine:3.14 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
 
 FROM ${ARCH}php:7.4-apache as build_other
 
diff --git a/webmails/roundcube/Dockerfile b/webmails/roundcube/Dockerfile
index fae02ce0..4d3e36df 100644
--- a/webmails/roundcube/Dockerfile
+++ b/webmails/roundcube/Dockerfile
@@ -2,7 +2,7 @@
 ARG ARCH=""
 ARG QEMU=other
 FROM ${ARCH}php:7.4-apache as build_arm
-ONBUILD COPY --from=balenalib/rpi-alpine:3.10 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
+ONBUILD COPY --from=balenalib/rpi-alpine:3.14 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
 
 FROM ${ARCH}php:7.4-apache as build_other