feat: do not bind SMTP client sockets to public addresses

This change reverts 06560dd071

Main reason for using the same address for sending
as the one used in DNS is to pass FCrDNS
(forward-confirmed reverse DNS) checks:
IP address used by SMTP client should resolve
to the domain which in turn resolves to the same IP.
chatmail relays don't do check reverse DNS
for incoming connections,
but other email servers may do and reject email
if the check does not pass.

Most chatmail relays only have one IP address per address family,
so this configuration does not change anything.

For chatmail relays that have multiple addresses
and only publishing one IP to DNS,
source address used for outgoing SMTP connections
should be the public IP.

This can be ensured by configuring the source
address in the routing table,
e.g. with the `src` argument
to `ip route add/change/replace` command.

Solving this by binding SMTP client address
on the application level prevents chatmail relays
from configuring alternative routes.

Besides, some chatmail relays are NATed
and NAT is responsible for translating the address to the public one,
in which case using `smtp_bind_address_enforce`
will result in unnecessarily deferring all mails.

chatmaild/src/chatmaild/config.py

@@ -1,4 +1,3 @@
-import os
 from pathlib import Path
 
 import iniconfig
@@ -47,8 +46,6 @@ class Config:
         )
         self.mtail_address = params.get("mtail_address")
         self.disable_ipv6 = params.get("disable_ipv6", "false").lower() == "true"
-        self.addr_v4 = os.environ.get("CHATMAIL_ADDR_V4", "")
-        self.addr_v6 = os.environ.get("CHATMAIL_ADDR_V6", "")
         self.acme_email = params.get("acme_email", "")
         self.imap_rawlog = params.get("imap_rawlog", "false").lower() == "true"
         self.imap_compress = params.get("imap_compress", "false").lower() == "true"

cmdeploy/src/cmdeploy/cmdeploy.py

@@ -101,9 +101,6 @@ def run_cmd(args, out):
     env["CHATMAIL_WEBSITE_ONLY"] = "True" if args.website_only else ""
     env["CHATMAIL_DISABLE_MAIL"] = "True" if args.disable_mail else ""
     env["CHATMAIL_REQUIRE_IROH"] = "True" if require_iroh else ""
-    if not args.dns_check_disabled:
-        env["CHATMAIL_ADDR_V4"] = remote_data.get("A") or ""
-        env["CHATMAIL_ADDR_V6"] = remote_data.get("AAAA") or ""
     deploy_path = importlib.resources.files(__package__).joinpath("run.py").resolve()
     pyinf = "pyinfra --dry" if args.dry_run else "pyinfra"
 

cmdeploy/src/cmdeploy/postfix/main.cf.j2

@@ -69,15 +69,6 @@ mynetworks = 127.0.0.0/8
 {% else %}
 mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
 {% endif %}
-{% if config.addr_v4 %}
-smtp_bind_address = {{ config.addr_v4 }}
-{% endif %}
-{% if config.addr_v6 %}
-smtp_bind_address6 = {{ config.addr_v6 }}
-{% endif %}
-{% if config.addr_v4 or config.addr_v6 %}
-smtp_bind_address_enforce = yes
-{% endif %}
 mailbox_size_limit = 0
 message_size_limit = {{config.max_message_size}}
 recipient_delimiter = +