diff --git a/ChangeLog b/ChangeLog
index dcb32dc9..9152cbb3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,16 @@
 	[Upcoming]
 
+	[4.2.0]
+
+	Add compatibility for OpenSSL across iRODS versions.
+
+	Add to the release Makefile Docker container builds for
+	iRODS 4.2.7, 4.2.11 and 4.2.12.
+
+	Add experimental CI build against iRODS 4.3-nightly.
+
+	Fix missing checksum file for the release tarball.
+
 	[4.1.0]
 	
 	Add iRODS 4.2.12 to test matrix.
diff --git a/release/Makefile b/release/Makefile
index 467b7f1d..dde9edd8 100644
--- a/release/Makefile
+++ b/release/Makefile
@@ -7,16 +7,15 @@ DOCKER_REGISTRY?=docker.io
 DOCKER_USER?=wsinpg
 endif
 
-BATON_VERSION?=4.0.1
-IRODS_VERSION?=4.2.11
-
 NOW=$(shell date --utc --iso-8601=seconds)
 
 DOCKER_PREFIX?=$(DOCKER_REGISTRY)/$(DOCKER_USER)
 DOCKER_ARGS ?= --platform linux/amd64 --progress=plain --rm
 .PHONY: clean push
 
-image_names += ub-18.04-baton-irods-$(IRODS_VERSION)
+image_names += ub-16.04-baton-irods-4.2.7
+image_names += ub-18.04-baton-irods-4.2.11
+image_names += ub-18.04-baton-irods-4.2.12
 
 git_url=$(shell git remote get-url origin)
 git_commit=$(shell git log --pretty=format:'%H' -n 1)
@@ -28,22 +27,58 @@ all: $(images)
 
 push: $(remote)
 
-ub-18.04-baton-irods-$(IRODS_VERSION).$(TAG): Dockerfile
+ub-16.04-baton-irods-4.2.7.$(TAG): ubuntu/16.04/Dockerfile
+	docker buildx build $(DOCKER_ARGS) \
+	--load \
+	--build-context source=.. \
+	--build-arg DOCKER_PREFIX=$(DOCKER_PREFIX) \
+	--build-arg DOCKER_IMAGE=$(subst .$(TAG),,$@) \
+	--build-arg DOCKER_TAG=$(TAG) \
+	--build-arg IRODS_VERSION="4.2.7" \
+	--build-arg BATON_VERSION=$(BATON_VERSION) \
+	--label org.opencontainers.image.title="iRODS 4.2.7 baton client, Ubuntu 16.04" \
+	--label org.opencontainers.image.source=$(git_url) \
+	--label org.opencontainers.image.revision=$(git_commit) \
+	--label org.opencontainers.image.version=$(TAG) \
+	--label org.opencontainers.image.created=$(NOW) \
+	--tag $(DOCKER_PREFIX)/ub-16.04-baton-irods-4.2.7:latest \
+	--tag $(DOCKER_PREFIX)/ub-16.04-baton-irods-4.2.7:$(TAG) --file $< .
+	touch $@
+
+ub-18.04-baton-irods-4.2.11.$(TAG): ubuntu/18.04/Dockerfile
+	docker buildx build $(DOCKER_ARGS) \
+	--load \
+	--build-context source=.. \
+	--build-arg DOCKER_PREFIX=$(DOCKER_PREFIX) \
+	--build-arg DOCKER_IMAGE=$(subst .$(TAG),,$@) \
+	--build-arg DOCKER_TAG=$(TAG) \
+	--build-arg IRODS_VERSION="4.2.11" \
+	--build-arg BATON_VERSION=$(BATON_VERSION) \
+	--label org.opencontainers.image.title="iRODS 4.2.11 baton client, Ubuntu 18.04" \
+	--label org.opencontainers.image.source=$(git_url) \
+	--label org.opencontainers.image.revision=$(git_commit) \
+	--label org.opencontainers.image.version=$(TAG) \
+	--label org.opencontainers.image.created=$(NOW) \
+	--tag $(DOCKER_PREFIX)/ub-18.04-baton-irods-4.2.11:latest \
+	--tag $(DOCKER_PREFIX)/ub-18.04-baton-irods-4.2.11:$(TAG) --file $< .
+	touch $@
+
+ub-18.04-baton-irods-4.2.12.$(TAG): ubuntu/18.04/Dockerfile
 	docker buildx build $(DOCKER_ARGS) \
 	--load \
 	--build-context source=.. \
 	--build-arg DOCKER_PREFIX=$(DOCKER_PREFIX) \
 	--build-arg DOCKER_IMAGE=$(subst .$(TAG),,$@) \
 	--build-arg DOCKER_TAG=$(TAG) \
-	--build-arg IRODS_VERSION=$(IRODS_VERSION) \
+	--build-arg IRODS_VERSION="4.2.12" \
 	--build-arg BATON_VERSION=$(BATON_VERSION) \
-	--label org.opencontainers.image.title="iRODS $(IRODS_VERSION) baton client, Ubuntu 18.04" \
+	--label org.opencontainers.image.title="iRODS 4.2.12 baton client, Ubuntu 18.04" \
 	--label org.opencontainers.image.source=$(git_url) \
 	--label org.opencontainers.image.revision=$(git_commit) \
 	--label org.opencontainers.image.version=$(TAG) \
 	--label org.opencontainers.image.created=$(NOW) \
-	--tag $(DOCKER_PREFIX)/ub-18.04-baton-irods-$(IRODS_VERSION):latest \
-	--tag $(DOCKER_PREFIX)/ub-18.04-baton-irods-$(IRODS_VERSION):$(TAG) --file $< .
+	--tag $(DOCKER_PREFIX)/ub-18.04-baton-irods-4.2.12:latest \
+	--tag $(DOCKER_PREFIX)/ub-18.04-baton-irods-4.2.12:$(TAG) --file $< .
 	touch $@
 
 %.$(TAG).pushed: %.$(TAG)
diff --git a/release/ubuntu/16.04/Dockerfile b/release/ubuntu/16.04/Dockerfile
new file mode 100644
index 00000000..48cb32a6
--- /dev/null
+++ b/release/ubuntu/16.04/Dockerfile
@@ -0,0 +1,133 @@
+# syntax=docker/dockerfile:1
+
+ARG BASE_IMAGE=ubuntu:16.04
+FROM $BASE_IMAGE as installer
+
+ARG IRODS_VERSION="4.2.7"
+
+RUN echo 'debconf debconf/frontend select Noninteractive' | debconf-set-selections && \
+    apt-get update && \
+    apt-get install -q -y --no-install-recommends \
+    apt-transport-https \
+    apt-utils \
+    ca-certificates \
+    curl \
+    dirmngr \
+    gnupg \
+    gnupg-agent \
+    lsb-release \
+    locales && \
+    locale-gen en_GB en_GB.UTF-8 && \
+    localedef -i en_GB -c -f UTF-8 -A /usr/share/locale/locale.alias en_GB.UTF-8
+
+ENV LANG=en_GB.UTF-8 \
+    LANGUAGE=en_GB \
+    LC_ALL=en_GB.UTF-8
+
+RUN curl -sSL https://packages.irods.org/irods-signing-key.asc | apt-key add - && \
+    echo "deb [arch=amd64] https://packages.irods.org/apt/ $(lsb_release -sc) main" |\
+    tee /etc/apt/sources.list.d/renci-irods.list && \
+    apt-get update && \
+    apt-get install -q -y --no-install-recommends \
+    irods-dev="${IRODS_VERSION}" \
+    irods-runtime="${IRODS_VERSION}"
+
+RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-keys "E1DD270288B4E6030699E45FA1715D88E1DF1F24" && \
+    echo "deb https://ppa.launchpadcontent.net/git-core/ppa/ubuntu $(lsb_release -sc) main" |\
+    tee /etc/apt/sources.list.d/git-core.list && \
+    apt-get update && \
+    apt-get install -q -y --no-install-recommends \
+    git
+
+# libdeflate-dev is not available on Ubuntu 16.04
+RUN apt-get update && \
+    apt-get install -q -y --no-install-recommends \
+    autoconf \
+    automake \
+    build-essential \
+    libtool \
+    pkg-config \
+    python3-sphinx \
+    libjansson-dev \
+    libcurl3-dev \
+    liblzma-dev \
+    zlib1g-dev
+
+COPY --from=source . /code
+
+WORKDIR /code
+
+ENV CPPFLAGS="-I/usr/include/irods"
+
+RUN autoreconf -fi && \
+    ./configure && \
+    make install && \
+    ldconfig
+
+FROM $BASE_IMAGE
+
+ARG DOCKER_IMAGE
+ARG DOCKER_TAG
+ARG IRODS_VERSION="4.2.7"
+
+ARG USER=baton
+ARG UID=1000
+ARG GID=$UID
+
+RUN echo 'debconf debconf/frontend select Noninteractive' | debconf-set-selections && \
+    apt-get update && \
+    apt-get install -q -y --no-install-recommends \
+    apt-transport-https \
+    apt-utils \
+    ca-certificates \
+    curl \
+    dirmngr \
+    gnupg \
+    gnupg-agent \
+    lsb-release \
+    locales && \
+    locale-gen en_GB en_GB.UTF-8 && \
+    localedef -i en_GB -c -f UTF-8 -A /usr/share/locale/locale.alias en_GB.UTF-8
+
+ENV LANG=en_GB.UTF-8 \
+    LANGUAGE=en_GB \
+    LC_ALL=en_GB.UTF-8
+
+RUN curl -sSL https://packages.irods.org/irods-signing-key.asc | apt-key add - && \
+    echo "deb [arch=amd64] https://packages.irods.org/apt/ $(lsb_release -sc) main" |\
+    tee /etc/apt/sources.list.d/renci-irods.list && \
+    apt-get update && \ 
+    apt-get install -q -y --no-install-recommends \
+    irods-runtime="${IRODS_VERSION}" \
+    jq \
+    libjansson4 \
+    libcurl3 \
+    liblzma5 \
+    zlib1g \
+    unattended-upgrades && \
+    unattended-upgrade -v && \
+    apt-get remove -q -y unattended-upgrades && \
+    apt-get autoremove -q -y && \
+    apt-get clean -q -y && \
+    rm -rf /var/lib/apt/lists/*
+
+# Copy the installed baton application
+COPY --from=installer /usr/local /usr/local
+
+# Copy the singularity-wrapper scripts
+COPY --from=installer /code/release/singularity-* /usr/local/bin
+COPY --from=installer /code/release/manifest.json /usr/local/etc/baton/manifest.json
+
+# Configure the singularity-wrapper script
+ENV MANIFEST_PATH="/usr/local/etc/baton/manifest.json"
+ENV DOCKER_IMAGE="$DOCKER_IMAGE"
+ENV DOCKER_TAG="$DOCKER_TAG"
+
+RUN ldconfig
+
+RUN groupadd --gid $GID $USER && \
+    useradd --uid $UID --gid $GID --shell /bin/bash --create-home $USER
+
+USER $USER
+
+CMD ["/bin/bash"]
diff --git a/release/Dockerfile b/release/ubuntu/18.04/Dockerfile
similarity index 99%
rename from release/Dockerfile
rename to release/ubuntu/18.04/Dockerfile
index d649e137..21cb191c 100644
--- a/release/Dockerfile
+++ b/release/ubuntu/18.04/Dockerfile
@@ -1,6 +1,6 @@
 # syntax=docker/dockerfile:1
 
-ARG BASE_IMAGE=ubuntu:bionic
+ARG BASE_IMAGE=ubuntu:18.04
 FROM $BASE_IMAGE as installer
 
 ARG IRODS_VERSION="4.2.11"
diff --git a/src/compat_checksum.c b/src/compat_checksum.c
index 3ef15caf..20b4a1ae 100644
--- a/src/compat_checksum.c
+++ b/src/compat_checksum.c
@@ -1,5 +1,5 @@
 /**
- * Copyright (C) 2015 Genome Research Ltd. All rights reserved.
+ * Copyright (C) 2015, 2023 Genome Research Ltd. All rights reserved.
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,42 +20,6 @@
 
 #include "compat_checksum.h"
 
-// #if IRODS_VERSION_INTEGER && IRODS_VERSION_INTEGER >= 4003000
-// MD5_CONTEXT* compat_MD5Init(baton_error_t *error) {
-//     const EVP_MD *md = EVP_md5();
-
-//     MD5_CONTEXT *context = EVP_MD_CTX_new();
-//     if (context == NULL) {
-//          set_baton_error(error, -1, "Failed to create an MD5 context");
-//          return NULL;
-//     }
-
-//     if (!EVP_DigestInit_ex(context, md, NULL)) {
-//         EVP_MD_CTX_free(context);
-//         set_baton_error(error, -1, "Failed to initialize an MD5 context");
-//         return NULL;
-//     }
-
-//     return context;
-// }
-
-// void compat_MD5Update(MD5_CONTEXT *context, unsigned char *input,
-//                       unsigned int len, baton_error_t *error) {
-//     if (!EVP_DigestUpdate(context, input, len)) {
-//         EVP_MD_CTX_free(context);
-//         set_baton_error(error, -1, "Failed to update an MD5 context");
-//     }
-// }
-
-// void compat_MD5Final(unsigned char digest[16], MD5_CONTEXT *context,
-//                     baton_error_t *error) {
-//     uint len = 16;
-//     if (!EVP_DigestFinal_ex(context, digest, &len)) {
-//         EVP_MD_CTX_free(context);
-//         set_baton_error(error, -1, "Failed to finalise an MD5 context");
-//     }
-// }
-// #else
 EVP_MD_CTX* compat_MD5Init(baton_error_t *error) {
     const EVP_MD *md = EVP_md5();
 
@@ -90,4 +54,3 @@ void compat_MD5Final(unsigned char digest[16], EVP_MD_CTX *context,
         set_baton_error(error, -1, "Failed to finalise an MD5 context");
     }
 }
-// #endif
diff --git a/src/compat_checksum.h b/src/compat_checksum.h
index 1efbb27d..d106d7dd 100644
--- a/src/compat_checksum.h
+++ b/src/compat_checksum.h
@@ -1,5 +1,5 @@
 /**
- * Copyright (C) 2015, 2016 Genome Research Ltd. All rights reserved.
+ * Copyright (C) 2015, 2016, 2023 Genome Research Ltd. All rights reserved.
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by