Retrieve GPG via keyserver in Dockerfile

docker/Dockerfile

@@ -1,10 +1,15 @@
 FROM debian:stretch
 
-RUN	apt-get update \
-	&& apt-get install -y --no-install-recommends gnupg dirmngr curl \
-	&& curl -fsSL http://rspamd.com/apt-stable/gpg.key | apt-key add - \
-	&& apt-get purge -y --auto-remove curl \
-	&& rm -rf /var/lib/apt/lists/*
+RUN	apt-get update && apt-get install -y --no-install-recommends gnupg dirmngr && rm -rf /var/lib/apt/lists/*
+
+RUN	set -x \
+# gpg: key FFA232EDBF21E25E: public key "Rspamd Nightly Builds (Rspamd Nightly Builds) <vsevolod@highsecure.ru>" imported
+	&& key='3FA347D5E599BE4595CA2576FFA232EDBF21E25E' \
+	&& export GNUPGHOME="$(mktemp -d)" \
+	&& gpg --keyserver ha.pool.sks-keyservers.net --recv-keys "$key" \
+	&& gpg --export "$key" > /etc/apt/trusted.gpg.d/rspamd.gpg \
+	&& rm -rf "$GNUPGHOME" \
+	&& apt-key list > /dev/null
 
 RUN	echo "deb http://rspamd.com/apt-stable/ stretch main" > /etc/apt/sources.list.d/rspamd.list