Ignore newlines and comment-lines in postfix overrides

To make postfix override files understandable and readable, users may
want to insert empty newlines and #-commented lines in their postfix
override files too. This will now ignore such bogus-lines and not send
them to `postconf`, which produced ugly errors in the past.

closes #1098

core/postfix/start.py

@@ -27,6 +27,10 @@ def start_podop():
         ("senderlogin", "url", url + "sender/login/§")
     ])
 
+def is_valid_postconf_line(line):
+    return not line.startswith("#") \
+            and not line == ''
+
 # Actual startup script
 os.environ["FRONT_ADDRESS"] = system.get_host_address_from_environment("FRONT", "front")
 os.environ["ADMIN_ADDRESS"] = system.get_host_address_from_environment("ADMIN", "admin")
@@ -38,10 +42,12 @@ for postfix_file in glob.glob("/conf/*.cf"):
 
 if os.path.exists("/overrides/postfix.cf"):
     for line in open("/overrides/postfix.cf").read().strip().split("\n"):
+        if is_valid_postconf_line(line):
             os.system('postconf -e "{}"'.format(line))
 
 if os.path.exists("/overrides/postfix.master"):
     for line in open("/overrides/postfix.master").read().strip().split("\n"):
+        if is_valid_postconf_line(line):
             os.system('postconf -Me "{}"'.format(line))
 
 for map_file in glob.glob("/overrides/*.map"):

towncrier/newsfragments/1098.misc

@@ -0,0 +1 @@
+Ignore newlines and comment-lines in postfix overrides - this means you can now make your override configfiles much more readable.