@@ -69,17 +69,23 @@ If DNSSEC is enabled at the box's domain name's registrar, the SSHFP record that
Outbound Mail
-------------
### Domain Policy Records
The basic protocols of email delivery did not plan for the presence of adversaries on the network. For a number of reasons it is not possible in most cases to guarantee that a connection to a recipient server is secure.
Domain policy records allow recipient MTAs to detect when the _domain_ part of incoming mail has been spoofed. All outbound mail is signed with [DKIM](https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail) and "quarantine" [DMARC](https://en.wikipedia.org/wiki/DMARC) records are automatically set in DNS. Receiving MTAs that implement DMARC will automatically quarantine mail that is "From:" a domain hosted by the box but which was not sent by the box. (Strong [SPF](https://en.wikipedia.org/wiki/Sender_Policy_Framework) records are also automatically set in DNS.) ([source](management/dns_update.py))
### DNSSEC
The first step in resolving the destination server for an email address is performing a DNS look-up for the MX record of the domain name. The box uses a locally-running [DNSSEC](https://en.wikipedia.org/wiki/DNSSEC)-aware nameserver to perform the lookup. If the domain name has DNSSEC enabled, DNSSEC guards against DNS records being tampered with.
### Encryption
The basic protocols of email delivery did not plan for the need for encryption. For a number of reasons it is not possible in most cases to guarantee that a connection to a recipient server is secure. However, the box --- along with the vast majority of mail servers --- uses [opportunistic encryption](https://en.wikipedia.org/wiki/Opportunistic_encryption), meaning the mail is encrypted in transit and protected from passive eavesdropping, but it is not protected from an active man-in-the-middle attack. Modern encryption settings will be used to the extent the recipient server supports them. ([source](setup/mail-postfix.sh))
The box (along with the vast majority of mail servers) uses [opportunistic encryption](https://en.wikipedia.org/wiki/Opportunistic_encryption), meaning the mail is encrypted in transit and protected from passive eavesdropping, but it is not protected from an active man-in-the-middle attack. Modern encryption settings will be used to the extent the recipient server supports them. ([source](setup/mail-postfix.sh))
### DANE
The box is [DNSSEC](https://en.wikipedia.org/wiki/DNSSEC)-aware (via a locally running DNSSEC-aware nameserver). When sending outbound mail, if the recipient's domain name supports DNSSEC and has published a [DANE TLSA](https://en.wikipedia.org/wiki/DNS-based_Authentication_of_Named_Entities) record, which contains a certificate fingerprint, the receiving MTA (server) must support TLS and its certificate must match the fingerprint. In other words, when a DANE TLSA record is published by the recipient, then on-the-wire encryption is forced between the box and the recipient MTA. ([source](setup/mail-postfix.sh))
If the recipient's domain name supports DNSSEC and has published a [DANE TLSA](https://en.wikipedia.org/wiki/DNS-based_Authentication_of_Named_Entities) record, then on-the-wire encryption is forced between the box and the recipient MTA and this encryption is not subject to a man-in-the-middle attack. The TLSA record contains a certificate fingerprint which the receiving MTA (server) must present to the box. ([source](setup/mail-postfix.sh))
### Domain Policy Records
Domain policy records allow recipient MTAs to detect when the _domain_ part of incoming mail has been spoofed. All outbound mail is signed with [DKIM](https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail) and "quarantine" [DMARC](https://en.wikipedia.org/wiki/DMARC) records are automatically set in DNS. Receiving MTAs that implement DMARC will automatically quarantine mail that is "From:" a domain hosted by the box but which was not sent by the box. (Strong [SPF](https://en.wikipedia.org/wiki/Sender_Policy_Framework) records are also automatically set in DNS.) ([source](management/dns_update.py))
