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Diffstat (limited to '')
| -rw-r--r-- | README_FILES/TLS_README | 120 |
1 files changed, 78 insertions, 42 deletions
diff --git a/README_FILES/TLS_README b/README_FILES/TLS_README index e7fd259..5e63554 100644 --- a/README_FILES/TLS_README +++ b/README_FILES/TLS_README @@ -1726,73 +1726,109 @@ describe the corresponding table syntax: nnoonnee No TLS. No additional attributes are supported at this level. mmaayy - Opportunistic TLS. The optional "ciphers", "exclude" and "protocols" - attributes (available for opportunistic TLS with Postfix >= 2.6) override - the "smtp_tls_ciphers", "smtp_tls_exclude_ciphers" and "smtp_tls_protocols" - configuration parameters. At this level and higher, the optional - "servername" attribute (available with Postfix >= 3.4) overrides the global - "smtp_tls_servername" parameter, enabling per-destination configuration of - the SNI extension sent to the remote SMTP server. + Opportunistic TLS. The optional "ciphers", "exclude", and "protocols" + attributes (available for opportunistic TLS with Postfix >= 2.6) and + "connection_reuse" attribute (Postfix >= 3.4) override the + "smtp_tls_ciphers", "smtp_tls_exclude_ciphers", "smtp_tls_protocols", and + "smtp_tls_connection_reuse" configuration parameters. At this level and + higher, the optional "servername" attribute (available with Postfix >= 3.4) + overrides the global "smtp_tls_servername" parameter, enabling per- + destination configuration of the SNI extension sent to the remote SMTP + server. The optional "enable_rpk" attribute (Postfix >= 3.9) overrides the + main.cf smtp_tls_enable_rpk parameter. When opportunistic TLS handshakes + fail, Postfix retries the connection with TLS disabled. This allows mail + delivery to sites with non-interoperable TLS implementations. eennccrryypptt Mandatory encryption. Mail is delivered only if the remote SMTP server offers STARTTLS and the TLS handshake succeeds. At this level and higher, the optional "protocols" attribute overrides the main.cf smtp_tls_mandatory_protocols parameter, the optional "ciphers" attribute - overrides the main.cf smtp_tls_mandatory_ciphers parameter, and the - optional "exclude" attribute (Postfix >= 2.6) overrides the main.cf - smtp_tls_mandatory_exclude_ciphers parameter. + overrides the main.cf smtp_tls_mandatory_ciphers parameter, the optional + "exclude" attribute (Postfix >= 2.6) overrides the main.cf + smtp_tls_mandatory_exclude_ciphers parameter, and the optional + "connection_reuse" attribute (Postfix >= 3.4) overrides the main.cf + smtp_tls_connection_reuse parameter. The optional "enable_rpk" attribute + (Postfix >= 3.9) overrides the main.cf smtp_tls_enable_rpk parameter. ddaannee Opportunistic DANE TLS. The TLS policy for the destination is obtained via TLSA records in DNSSEC. If no TLSA records are found, the effective security level used is may. If TLSA records are found, but none are usable, the effective security level is encrypt. When usable TLSA records are - obtained for the remote SMTP server, SSLv2+3 are automatically disabled - (see smtp_tls_mandatory_protocols), and the server certificate must match - the TLSA records. RFC 7672 (DANE) TLS authentication and DNSSEC support is - available with Postfix 2.11 and later. + obtained for the remote SMTP server, the server certificate must match the + TLSA records (and the SNI name is unconditionally set to the TLSA base + domain). RFC 7672 (DANE) TLS authentication and DNSSEC support is available + with Postfix 2.11 and later. The optional "connection_reuse" attribute + (Postfix >= 3.4) overrides the main.cf smtp_tls_connection_reuse parameter. + When the effective security level used is may, the optional "ciphers", + "exclude", and "protocols" attributes (Postfix >= 2.6) override the + "smtp_tls_ciphers", "smtp_tls_exclude_ciphers", and "smtp_tls_protocols" + configuration parameters. When the effective security level used is + encrypt, the optional "ciphers", "exclude", and "protocols" attributes + (Postfix >= 2.6) override the "smtp_tls_mandatory_ciphers", + "smtp_tls_mandatory_exclude_ciphers", and "smtp_tls_mandatory_protocols" + configuration parameters. ddaannee--oonnllyy Mandatory DANE TLS. The TLS policy for the destination is obtained via TLSA records in DNSSEC. If no TLSA records are found, or none are usable, no connection is made to the server. When usable TLSA records are obtained for - the remote SMTP server, SSLv2+3 are automatically disabled (see - smtp_tls_mandatory_protocols), and the server certificate must match the - TLSA records. RFC 7672 (DANE) TLS authentication and DNSSEC support is - available with Postfix 2.11 and later. + the remote SMTP server, the server certificate must match the TLSA records. + RFC 7672 (DANE) TLS authentication and DNSSEC support is available with + Postfix 2.11 and later. The optional "ciphers", "exclude", and "protocols" + attributes (Postfix >= 2.6) override the "smtp_tls_mandatory_ciphers", + "smtp_tls_mandatory_exclude_ciphers", and "smtp_tls_mandatory_protocols" + configuration parameters. The optional "connection_reuse" attribute + (Postfix >= 3.4) overrides the main.cf smtp_tls_connection_reuse parameter. ffiinnggeerrpprriinntt Certificate fingerprint verification. Available with Postfix 2.5 and later. At this security level, there are no trusted Certification Authorities. The certificate trust chain, expiration date, ... are not checked. Instead, the - optional mmaattcchh attribute, or else the main.cf - ssmmttpp__ttllss__ffiinnggeerrpprriinntt__cceerrtt__mmaattcchh parameter, lists the server certificate - fingerprints or public key fingerprints (Postfix 2.9 and later). The digest - algorithm used to calculate fingerprints is selected by the - ssmmttpp__ttllss__ffiinnggeerrpprriinntt__ddiiggeesstt parameter. Multiple fingerprints can be - combined with a "|" delimiter in a single match attribute, or multiple - match attributes can be employed. The ":" character is not used as a - delimiter as it occurs between each pair of fingerprint (hexadecimal) - digits. + optional "match" attribute, or else the main.cf + ssmmttpp__ttllss__ffiinnggeerrpprriinntt__cceerrtt__mmaattcchh parameter, lists the certificate + fingerprints or the public key fingerprints (Postfix 2.9 and later) of + acceptable server certificates. The digest algorithm used to calculate the + fingerprint is selected by the ssmmttpp__ttllss__ffiinnggeerrpprriinntt__ddiiggeesstt parameter. + Multiple fingerprints can be combined with a "|" delimiter in a single + match attribute, or multiple match attributes can be employed. The ": + " character is not used as a delimiter as it occurs between each pair of + fingerprint (hexadecimal) digits. The optional "ciphers", "exclude", and + "protocols" attributes (Postfix >= 2.6) override the + "smtp_tls_mandatory_ciphers", "smtp_tls_mandatory_exclude_ciphers", and + "smtp_tls_mandatory_protocols" configuration parameters. The optional + "connection_reuse" attribute (Postfix >= 3.4) overrides the main.cf + smtp_tls_connection_reuse parameter. The optional "enable_rpk" attribute + (Postfix >= 3.9) overrides the main.cf smtp_tls_enable_rpk parameter. vveerriiffyy Mandatory server certificate verification. Mail is delivered only if the - TLS handshake succeeds, if the remote SMTP server certificate can be - validated (not expired or revoked, and signed by a trusted Certification - Authority), and if the server certificate name matches the optional "match" - attribute (or the main.cf smtp_tls_verify_cert_match parameter value when - no optional "match" attribute is specified). With Postfix >= 2.11 the + TLS handshake succeeds, the remote SMTP server certificate chain can be + validated, and a DNS name in the certificate matches the specified match + criteria. At this security level, DNS MX lookups are presumed to be secure + enough, and the name verified in the server certificate is potentially + obtained via unauthenticated DNS MX lookups. The server certificate name + must match either the optional "match" attribute, or else the main.cf + smtp_tls_verify_cert_match parameter value. With Postfix >= 2.11 the "tafile" attribute optionally modifies trust chain verification in the same manner as the "smtp_tls_trust_anchor_file" parameter. The "tafile" attribute may be specified multiple times to load multiple trust-anchor - files. + files. The optional "connection_reuse" attribute (Postfix >= 3.4) overrides + the main.cf smtp_tls_connection_reuse parameter. sseeccuurree Secure certificate verification. Mail is delivered only if the TLS - handshake succeeds, and DNS forgery resistant remote SMTP certificate - verification succeeds (not expired or revoked, and signed by a trusted - Certification Authority), and if the server certificate name matches the - optional "match" attribute (or the main.cf smtp_tls_secure_cert_match - parameter value when no optional "match" attribute is specified). With - Postfix >= 2.11 the "tafile" attribute optionally modifies trust chain - verification in the same manner as the "smtp_tls_trust_anchor_file" - parameter. The "tafile" attribute may be specified multiple times to load - multiple trust-anchor files. + handshake succeeds, the remote SMTP server certificate chain can be + validated, and a DNS name in the certificate matches the specified match + criteria. At this security level, DNS MX lookups, though potentially used + to determine the candidate next-hop gateway IP addresses, are nnoott presumed + to be secure enough for TLS peername verification. Instead, the default + name verified in the server certificate is obtained directly from the next- + hop, or is explicitly specified via the optional "match" attribute which + overrides the main.cf smtp_tls_secure_cert_match parameter. The optional + "ciphers", "exclude", and "protocols" attributes (Postfix >= 2.6) override + the "smtp_tls_mandatory_ciphers", "smtp_tls_mandatory_exclude_ciphers", and + "smtp_tls_mandatory_protocols" configuration parameters. With Postfix >= + 2.11 the "tafile" attribute optionally modifies trust chain verification in + the same manner as the "smtp_tls_trust_anchor_file" parameter. The "tafile" + attribute may be specified multiple times to load multiple trust-anchor + files. The optional "connection_reuse" attribute (Postfix >= 3.4) overrides + the main.cf smtp_tls_connection_reuse parameter. Notes: * The "match" attribute is especially useful to verify TLS certificates for |