Switching to alpine:3.12 and use fetchmail from alpine repository

alpine3:12 provides fetchmail 6.4.5, so building fetchmail from alpha branch
is not needed anymore (ssl wrapped mode issue fixed) since 6.4.2

optional/fetchmail/Dockerfile

@@ -1,17 +1,4 @@
-# First stage: Build
+ARG DISTRO=alpine:3.12
-ARG DISTRO=alpine:3.10
-FROM $DISTRO as builder
-
-# build dependencies
-RUN apk add --no-cache curl tar xz autoconf git gettext build-base openssl openssl-dev
-
-RUN curl -L 'https://sourceforge.net/projects/fetchmail/files/branch_7-alpha/fetchmail-7.0.0-alpha6.tar.xz/download' | tar xJ
-RUN cd fetchmail-7.0.0-alpha6 && \
-    sed -i -e 's/SSLv3_client_method/SSLv23_client_method/' socket.c && \
-    ./configure --with-ssl --prefix /usr/local --disable-nls && \
-    make
-
-ARG DISTRO=alpine:3.10
 FROM $DISTRO
 
 # python3 shared with most images
@@ -20,13 +7,11 @@ RUN apk add --no-cache \
   && pip3 install --upgrade pip
 
 # Image specific layers under this line
-RUN apk add --no-cache ca-certificates openssl \
+RUN apk add --no-cache fetchmail ca-certificates openssl \
  && pip3 install requests
 
-COPY --from=builder /fetchmail-7.0.0-alpha6/fetchmail /usr/local/bin
 COPY fetchmail.py /fetchmail.py
 
-RUN adduser -D fetchmail
 USER fetchmail
 
 CMD ["/fetchmail.py"]

optional/fetchmail/fetchmail.py

@@ -56,7 +56,7 @@ def run(debug):
         for fetch in fetches:
             fetchmailrc = ""
             options = "options antispam 501, 504, 550, 553, 554"
-            options += " sslmode wrapped" if fetch["tls"] else ""
+            options += " ssl" if fetch["tls"] else ""
             options += " keep" if fetch["keep"] else " fetchall"
             fetchmailrc += RC_LINE.format(
                 user_email=escape_rc_string(fetch["user_email"]),