breaking: Refactor getmail support (#4156)

Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>
Co-authored-by: Georg Lauterbach <44545919+georglauterbach@users.noreply.github.com>

target/getmail/getmail-service.sh

@@ -0,0 +1,47 @@
+#!/bin/bash
+
+# shellcheck source=../scripts/helpers/log.sh
+source /usr/local/bin/helpers/log.sh
+
+# Directory, where "oldmail" files are stored.
+# getmail stores its state - its "memory" of what it has seen in your POP/IMAP account - in the oldmail files.
+GETMAIL_DIR=/var/lib/getmail
+
+# Kill all child processes on EXIT.
+# Otherwise 'supervisorctl restart getmail' leads to zombie 'sleep' processes.
+trap 'pkill --parent ${$}' EXIT
+
+function _syslog_error() {
+  logger --priority mail.err --tag getmail "${1}"
+}
+
+function _stop_service() {
+  _syslog_error "Stopping service"
+  exec supervisorctl stop getmail
+}
+
+# Verify the correct value for GETMAIL_POLL. Valid are any numbers greater than 0.
+if [[ ! ${GETMAIL_POLL} =~ ^[0-9]+$ ]] || [[ ${GETMAIL_POLL} -lt 1 ]]; then
+  _syslog_error "Invalid value for GETMAIL_POLL: ${GETMAIL_POLL}"
+  _stop_service
+fi
+
+# If no matching filenames are found, and the shell option nullglob is disabled, the word is left unchanged.
+# If the nullglob option is set, and no matches are found, the word is removed.
+shopt -s nullglob
+
+# Run each getmailrc periodically.
+while :; do
+  for RC_FILE in /etc/getmailrc.d/*; do
+    _log 'debug' "Processing ${RC_FILE}"
+    getmail --getmaildir "${GETMAIL_DIR}" --rcfile "${RC_FILE}"
+  done
+
+  # Stop service if no configuration is found.
+  if [[ -z ${RC_FILE} ]]; then
+    _syslog_error 'No configuration found'
+    _stop_service
+  fi
+
+  sleep "${GETMAIL_POLL}m"
+done

target/getmail/getmailrc_general

@@ -1,3 +1,5 @@
+# https://getmail6.org/configuration.html#conf-options
+
 [options]
 verbose = 0
 read_all = false
@@ -5,3 +7,5 @@ delete = false
 max_messages_per_session = 500
 received = false
 delivered_to = false
+message_log_syslog = true
+