SMTP proxy with "STARTTLS only" accepts unencrypted mail
mdounin at mdounin.ru
Tue Jun 4 13:49:34 UTC 2019
On Mon, Jun 03, 2019 at 10:16:20PM +0200, Marcus wrote:
> I try to use NGiNX 1.10.3-1+deb9u2 (Debian 9 version) as SMTP proxy in
> front of a postfix server. I defined one server that should accept
> encrypted connections only. Therefore I set "starttls only".
> But this server accepts plaintext mails also. If I use telnet to test
> the proxy it provides STARTTLS but I can relay a mail without using it.
Currently, "starttls" is only enforced for authentication, but not
for non-authenticated mail delivery, as with "smtp_auth none" in
your config. If you want to reject all non-encrypted
non-authenticated mail delivery, you can do so using an auth_http
Recently discussed here:
More information about the nginx