4 ms·
> Could you explain why this should be necessary when email communication between the servers and clients is already encrypted via SSL/TLS? Can they bypass that
by zrm 11y ago
> Could you explain why this should be necessary when email communication between the servers and clients is already encrypted via SSL/TLS? Can they bypass that? (And if so how?)
RFC2487 Section 5:
A publicly-referenced SMTP server MUST NOT require use of the
STARTTLS extension in order to deliver mail locally. This rule
prevents the STARTTLS extension from damaging the interoperability of
the Internet's SMTP infrastructure. A publicly-referenced SMTP server
is an SMTP server which runs on port 25 of an Internet host listed in
the MX record (or A record if an MX record is not present) for the
domain name on the right hand side of an Internet mail address.
In other words, internet mail servers are required to allow a trivial downgrade to plaintext by a MITM attacker.
- btgeekboy 11y agoAnd if you don't follow the RFC, the internet police will come after you! Yes, I am aware of the RFC2119 meaning of "MUST NOT." In reality, nothing prevents the servers from disallowing that downgrade, except that they may not be interoperable with other servers on the internet. If the operator of the server wishes to make that tradeoff, then requiring STARTTLS is an option.
- zrm 11y agoIf you don't follow the RFC then people will email you from gmail saying "I tried to send you mail from my company's mail server and it didn't work", other people will submit a github issue to your project saying they couldn't email you, and when you try to subscribe to one of djb's mailing lists you'll get a response from your mail server saying it couldn't deliver the message. That is what actually happened when I tried it.
- spc476 11y agoAnd I subscribed to a mailing list years ago that suddenly went TLS-mandatory (for incoming email---it doesn't demand TLS when sending email) and now I can't even unsubscribe from the list.
- LinuxBender 11y agoMy mail server forces TLS and strong ciphers. Try it out. postmaster@ohdns.org You may also test using that address on checktls[1] [1] http://www.checktls.com/perl/TestReceiver.pl?ASSURETLS http://www.checktls.com/perl/TestReceiver.pl?ASSURETLS I receive emails from whitehouse.gov and other .gov sites just fine, so they seem to be ok with it. Also, my self signed CA cert and self signed server cert regenerate every hour for those that do not support PFS. My DH primes regenerate periodically. If you are someone that needs to assure you are talking to me, you don't need a CA. Instead, you test the connection to me from multiple ISP's before and after you send me an email. For real security, you would encrypt the payload. Maybe an encrypted 7zip inside a PGP encrypted message.