Add support for bidirectional mail alias controls

This is an extension of #427. Building on that change it adds support in the
aliases table for flagging aliases as:
 1. Applicable to inbound and outbound mail.
 2. Applicable to inbound mail only.
 3. Applicable to outbound mail only.
 4. Disabled.

The aliases UI is also updated to allow administrators to set the direction of
each alias.

Using this extra information, the sqlite queries executed by Postfix are
updated so only the relevant alias types are checked.

The goal and result of this change is that outbound-only catch-all aliases can
now be defined (in fact catch-all aliases of any type can be defined).

This allow us to continue supporting relaying as described at
https://mailinabox.email/advanced-configuration.html#relay
without requiring that administrators either create regular aliases for each
outbound *relay* address, or that they create a catch-all alias and then face a
flood of spam.

I have tested the code as it is in this commit and fixed every issue I found,
so in that regard the change is complete. However I see room for improvement
in terms of updating terminology to make the UI etc. easier to understand.
I'll make those changes as subsequent commits so that this tested checkpoint is
not lost, but also so they can be rejected independently of the actual change
if not wanted.

management/mailconfig.py

@@ -181,13 +181,13 @@ def get_admins(env):
 	return users
 
 def get_mail_aliases(env):
-	# Returns a sorted list of tuples of (alias, forward-to string).
+	# Returns a sorted list of tuples of (alias, forward-to string, applies-to-inbound-mail, applies-to-outbound-mail).
 	c = open_database(env)
-	c.execute('SELECT source, destination FROM aliases')
-	aliases = { row[0]: row[1] for row in c.fetchall() } # make dict
+	c.execute('SELECT source, destination, applies_inbound, applies_outbound FROM aliases')
+	aliases = { row[0]: row[1:4] for row in c.fetchall() } # make dict
 
 	# put in a canonical order: sort by domain, then by email address lexicographically
-	aliases = [ (source, aliases[source]) for source in utils.sort_email_addresses(aliases.keys(), env) ]
+	aliases = [ (source,) + aliases[source] for source in utils.sort_email_addresses(aliases.keys(), env) ]
 	return aliases
 
 def get_mail_aliases_ex(env):
@@ -202,6 +202,8 @@ def get_mail_aliases_ex(env):
 	#         source: "name@domain.tld", # IDNA-encoded
 	#         source_display: "name@domain.tld", # full Unicode
 	#         destination: ["target1@domain.com", "target2@domain.com", ...],
+	#         applies_inbound: True|False
+	#         applies_outbound: True|False
 	#         required: True|False
 	#       },
 	#       ...
@@ -212,7 +214,7 @@ def get_mail_aliases_ex(env):
 
 	required_aliases = get_required_aliases(env)
 	domains = {}
-	for source, destination in get_mail_aliases(env):
+	for source, destination, applies_inbound, applies_outbound in get_mail_aliases(env):
 		# get alias info
 		domain = get_domain(source)
 		required = (source in required_aliases)
@@ -227,6 +229,8 @@ def get_mail_aliases_ex(env):
 			"source": source,
 			"source_display": prettify_idn_email_address(source),
 			"destination": [prettify_idn_email_address(d.strip()) for d in destination.split(",")],
+			"applies_inbound": True if applies_inbound == 1 else False,
+			"applies_outbound": True if applies_outbound == 1 else False,
 			"required": required,
 		})
 
@@ -250,7 +254,7 @@ def get_mail_domains(env, filter_aliases=lambda alias : True):
 	# configured on the system.
 	return set(
 		   [get_domain(addr, as_unicode=False) for addr in get_mail_users(env)]
-		 + [get_domain(source, as_unicode=False) for source, target in get_mail_aliases(env) if filter_aliases((source, target)) ]
+		 + [get_domain(source, as_unicode=False) for source, *_ in get_mail_aliases(env) if filter_aliases(source) ]
 		 )
 
 def add_mail_user(email, pw, privs, env):
@@ -406,7 +410,7 @@ def add_remove_mail_user_privilege(email, priv, action, env):
 
 	return "OK"
 
-def add_mail_alias(source, destination, env, update_if_exists=False, do_kick=True):
+def add_mail_alias(source, destination, applies_inbound, applies_outbound, env, update_if_exists=False, do_kick=True):
 	# convert Unicode domain to IDNA
 	source = sanitize_idn_email_address(source)
 
@@ -460,13 +464,13 @@ def add_mail_alias(source, destination, env, update_if_exists=False, do_kick=Tru
 	# save to db
 	conn, c = open_database(env, with_connection=True)
 	try:
-		c.execute("INSERT INTO aliases (source, destination) VALUES (?, ?)", (source, destination))
+		c.execute("INSERT INTO aliases (source, destination, applies_inbound, applies_outbound) VALUES (?, ?, ?, ?)", (source, destination, 1 if applies_inbound else 0, 1 if applies_outbound else 0))
 		return_status = "alias added"
 	except sqlite3.IntegrityError:
 		if not update_if_exists:
 			return ("Alias already exists (%s)." % source, 400)
 		else:
-			c.execute("UPDATE aliases SET destination = ? WHERE source = ?", (destination, source))
+			c.execute("UPDATE aliases SET destination = ?, applies_inbound = ?, applies_outbound = ? WHERE source = ?", (destination, 1 if applies_inbound else 0, 1 if applies_outbound else 0, source))
 			return_status = "alias updated"
 
 	conn.commit()
@@ -507,8 +511,8 @@ def get_required_aliases(env):
 	# email on that domain are the required aliases or a catch-all/domain-forwarder.
 	real_mail_domains = get_mail_domains(env,
 		filter_aliases = lambda alias :
-			not alias[0].startswith("postmaster@") and not alias[0].startswith("admin@")
-			and not alias[0].startswith("@")
+			not alias.startswith("postmaster@") and not alias.startswith("admin@")
+			and not alias.startswith("@")
 			)
 
 	# Create postmaster@ and admin@ for all domains we serve mail on.
@@ -541,14 +545,14 @@ def kick(env, mail_result=None):
 			return
 
 		# Does this alias exists?
-		for s, t in existing_aliases:
+		for s, *_ in existing_aliases:
 			if s == source:
 				return
 
 		# Doesn't exist.
 		administrator = get_system_administrator(env)
 		if source == administrator: return # don't make an alias from the administrator to itself --- this alias must be created manually
-		add_mail_alias(source, administrator, env, do_kick=False)
+		add_mail_alias(source, administrator, True, True, env, do_kick=False)
 		results.append("added alias %s (=> %s)\n" % (source, administrator))
 
 	for alias in required_aliases:
@@ -556,7 +560,7 @@ def kick(env, mail_result=None):
 
 	# Remove auto-generated postmaster/admin on domains we no
 	# longer have any other email addresses for.
-	for source, target in existing_aliases:
+	for source, target, *_ in existing_aliases:
 		user, domain = source.split("@")
 		if user in ("postmaster", "admin") \
 			and source not in required_aliases \