Pin Alpine 3.7 to preserve the Postfix version

core/admin/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3-alpine
+FROM python:3-alpine3.7
 
 RUN mkdir -p /app
 WORKDIR /app

core/dovecot/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:edge
+FROM alpine:3.7
 
 RUN echo "@testing http://nl.alpinelinux.org/alpine/edge/testing" >> /etc/apk/repositories \
  && apk add --no-cache \

core/nginx/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:edge
+FROM alpine:3.7
 
 RUN apk add --no-cache nginx nginx-mod-mail python py-jinja2 certbot openssl
 

core/none/Dockerfile

@@ -1,5 +1,5 @@
 # This is an idle image to dynamically replace any component if disabled.
 
-FROM alpine
+FROM alpine:3.7
 
 CMD sleep 1000000d

optional/clamav/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:edge
+FROM alpine:3.7
 
 RUN apk add --no-cache clamav rsyslog wget clamav-libunrar
 

optional/radicale/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:edge
+FROM alpine:3.7
 
 RUN echo "@testing http://nl.alpinelinux.org/alpine/edge/testing" >> /etc/apk/repositories \
  && apk add --no-cache radicale@testing py-dulwich@testing

services/fetchmail/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:alpine
+FROM python:alpine3.7
 
 RUN apk add --no-cache fetchmail ca-certificates
 

services/rspamd/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:edge
+FROM alpine:3.7
 
 RUN apk add --no-cache python py-jinja2 rspamd rspamd-controller rspamd-proxy ca-certificates