This is the Postfix 3.7 (stable) release. The stable Postfix release is called postfix-3.7.x where 3=major release number, 7=minor release number, x=patchlevel. The stable release never changes except for patches that address bugs or emergencies. Patches change the patchlevel and the release date. New features are developed in snapshot releases. These are called postfix-3.8-yyyymmdd where yyyymmdd is the release date (yyyy=year, mm=month, dd=day). Patches are never issued for snapshot releases; instead, a new snapshot is released. The mail_release_date configuration parameter (format: yyyymmdd) specifies the release date of a stable release or snapshot release. If you upgrade from Postfix 3.5 or earlier, read RELEASE_NOTES-3.6 before proceeding. License change --------------- This software is distributed with a dual license: in addition to the historical IBM Public License 1.0, it is now also distributed with the more recent Eclipse Public License 2.0. Recipients can choose to take the software under the license of their choice. Those who are more comfortable with the IPL can continue with that license. Incompatibility with Postfix 3.8.5, 3.7.10, 3.6.14, and 3.5.24 ============================================================== Improvements for outbound SMTP smuggling defense: - With "cleanup_replace_stray_cr_lf = yes" (the default), the cleanup daemon replaces each stray or character in message content with a space character. The replacement happens before any other content management (header/body_checks, Milters, etc). This prevents outbound SMTP smuggling, where an attacker uses Postfix to send email containing a non-standard End-of-DATA sequence, to exploit inbound SMTP smuggling at a vulnerable remote SMTP server. This also improves the remote evaluation of Postfix-added DKIM and other signatures, as the evaluation result will not depend on how a remote email server handles stray or characters. This feature applies to all email that Postfix locally or remotely sends out. It is not allowlisted based on client identity. Major changes with Postfix 3.8.5, 3.7.10, 3.6.14, and 3.5.24 ============================================================ Improvements for inbound SMTP smuggling defense: - Better compatibility: the recommended setting "smtpd_forbid_bare_newline = normalize" requires the standard End-of-DATA sequence ., but allows bare newlines from SMTP clients, maintaining more compatibility with existing infrastructure. - Improved logging for rejected input (it now includes queue ID, helo, mail, and rcpt, if available). - The setting "smtpd_forbid_bare_newline = reject" requires that input lines end in , requires the standard End-of-DATA sequence ., and rejects a command or message that contains a bare newline. To disconnect the client, specify "smtpd_forbid_bare_newline_reject_code = 521". - The Postfix SMTP server no longer strips extra as in ., to silence false alarms from test tools that send attack sequences that real mail servers cannot send. Details at https://www.postfix.org/false-smuggling-claims.html - The old setting "yes" has become an alias for "normalize". - The old setting "no" has not changed, and allows SMTP smuggling. The recommended settings are now: # Require the standard End-of-DATA sequence .. # Otherwise, allow bare and process it as if the client sent # . # # This maintains compatibility with many legitimate SMTP client # applications that send a mix of standard and non-standard line # endings, but will fail to receive email from client implementations # that do not terminate DATA content with the standard End-of-DATA # sequence .. # # Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions. # The example below allowlists SMTP clients in trusted networks. # smtpd_forbid_bare_newline = normalize smtpd_forbid_bare_newline_exclusions = $mynetworks Alternative settings: # Reject input lines that contain and log a "bare received" # error. Require that input lines end in , and require the # standard End-of-DATA sequence .. # # This will reject email from SMTP clients that send any non-standard # line endings such as web applications, netcat, or load balancer # health checks. # # This will also reject email from services that use BDAT to send # MIME text containing a bare newline (RFC 3030 Section 3 requires # canonical MIME format for text message types, defined in RFC 2045 # Sections 2.7 and 2.8). # # Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions. # The example below allowlists SMTP clients in trusted networks. # smtpd_forbid_bare_newline = reject smtpd_forbid_bare_newline_exclusions = $mynetworks # # Alternatively, in the case of BDAT violations, BDAT can be selectively # disabled with smtpd_discard_ehlo_keyword_address_maps, or globally # disabled with smtpd_discard_ehlo_keywords. # # smtpd_discard_ehlo_keyword_address_maps = cidr:/path/to/file # /path/to/file: # 10.0.0.0/24 chunking, silent-discard # smtpd_discard_ehlo_keywords = chunking, silent-discard Major changes with Postfix 3.7.6 ================================ Security: the Postfix SMTP server optionally disconnects remote SMTP clients that violate RFC 2920 (or 5321) command pipelining constraints. The server replies with "554 5.5.0 Error: SMTP protocol synchronization" and logs the unexpected remote SMTP client input. Specify "smtpd_forbid_unauth_pipelining = yes" to enable. This feature is enabled by default in Postfix 3.9 and later. Workaround to limit collateral damage from OS distributions that crank up security to 11, increasing the number of plaintext email deliveries. This introduces basic OpenSSL configuration file support, with two new parameters "tls_config_file" and "tls_config_name". Details are in the postconf(5) manpage under "tls_config_file" and "tls_config_name". Bugfix for messages not delivered after "warning: Unexpected record type 'X' ============================================================================ Due to a bug introduced in Postfix 3.7.0, a message could falsely be flagged as corrupt with "warning: Unexpected record type 'X'". Such messages were moved to the "corrupt" queue directory, where they may still be found. See below for instructions to deal with these falsely flagged messages. This could happen for messages with 5000 or more recipients, or with fewer recipients on a busy mail server. The problem was first reported by Frank Brendel, reproduced by John Alex. A file in the "corrupt" queue directory may be inspected with the command "postcat /var/spool/postfix/corrupt/. If delivery of the file is still desired, the file can be moved back to /var/spool/postfix/incoming after updating Postfix and executing "postfix reload". Major changes - configuration ----------------------------- [Feature 20210605] Support to inline the content of small cidr:, pcre:, and regexp: tables in Postfix parameter values. Example: smtpd_forbidden_commands = CONNECT GET POST regexp:{{/^[^A-Z]/ Thrash}} This is the new smtpd_forbidden_commands default value. It will immediately disconnect a remote SMTP client when a command does not start with a letter (a-z or A-Z). The basic syntax is: /etc/postfix/main.cf: parameter = .. map-type:{ { rule-1 }, { rule-2 } .. } .. /etc/postfix/master.cf: .. -o { parameter = .. map-type:{ { rule-1 }, { rule-2 } .. } .. } .. where map-type is one of cidr, pcre, or regexp. Postfix ignores whitespace after '{' and before '}', and writes each rule as one text line to a nameless in-memory file: in-memory file: rule-1 rule-2 .. Postfix parses the result as if it is a file in /etc/postfix. Note: if a rule contains $, specify $$ to keep Postfix from trying to do $name expansion as it evaluates the parameter value. Major changes - lmdb support ---------------------------- [Feature 20210605] Overhauled the LMDB client's error handling, and added integration tests for future-proofing. There are no visible changes in documented behavior. Major changes - logging ----------------------- [Feature 20210815] To make the maillog_file feature more useful, the postlog(1) command is now set-gid postdrop, so that unprivileged programs can use it to write logging through the postlogd(8) daemon. This required hardening the postlog(1) command against privilege escalation attacks. DO NOT turn on the set-gid bit with older postlog(1) implementations. Major changes - pcre2 support ----------------------------- [Feature 20211127] Support for the pcre2 library (the legacy pcre library is no longer maintained). The Postfix build procedure automatically detects if the pcre2 library is installed, and if it is unavailable, the Postfix build procedure will detect if the legacy pcre library is installed. See PCRE_README if you need to build Postfix with a specific library. Visible differences: some error messages may have a different text, and the 'X' pattern flag is no longer supported with pcre2. Major changes - security ------------------------ [Feature 20220102] Postfix programs now randomize the initial state of in-memory hash tables, to defend against hash collision attacks involving a large number of attacker-chosen lookup keys. Presently, the only known opportunity for such attacks involves remote SMTP client IPv6 addresses in the anvil(8) service. The attack would require making hundreds of short-lived connections per second from thousands of different IP addresses, because the anvil(8) service drops inactive counters after 100s. Other in-memory hash tables with attacker-chosen lookup keys are by design limited in size. The fix is cheap, and therefore implemented for all Postfix in-memory hash tables. Problem reported by Pascal Junod. [Feature 20211030] The postqueue command now sanitizes non-printable characters (such as newlines) in strings before they are formatted as json or as legacy output. These outputs are piped into other programs that are run by administrative users. This closes a hypothetical opportunity for privilege escalation. [Feature 20210815] Updated defense against remote clients or servers that 'trickle' SMTP or LMTP traffic, based on per-request deadlines and minimum data rates. Per-request deadlines: The new {smtpd,smtp,lmtp}_per_request_deadline parameters replace {smtpd,smtp,lmtp}_per_record_deadline, with backwards compatible default settings. This defense is enabled by default in the Postfix SMTP server in case of overload. The new smtpd_per_record_deadline parameter limits the combined time for the Postfix SMTP server to receive a request and to send a response, while the new {smtp,lmtp}_per_record_deadline parameters limit the combined time for the Postfix SMTP or LMTP client to send a request and to receive a response. Minimum data rates: The new smtpd_min_data_rate parameter enforces a minimum plaintext data transfer rate for DATA and BDAT requests, but only when smtpd_per_record_deadline is enabled. After a read operation transfers N plaintext bytes (possibly after TLS decryption), and after the DATA or BDAT request deadline is decreased by the elapsed time of that read operation, the DATA or BDAT request deadline is increased by N/smtpd_min_data_rate seconds. However, the deadline is never increased beyond the smtpd_timeout value. The default minimum data rate is 500 (bytes/second) but is still subject to change. The new {smtp,lmtp}_min_data_rate parameters enforce the corresponding minimum DATA transfer rates for the Postfix SMTP and LMTP client. Major changes - tls support --------------------------- [Cleanup 20220121] The new tlsproxy_client_security_level parameter replaces tlsproxy_client_level, and the new tlsproxy_client_policy_maps parameter replaces tlsproxy_client_policy. This is for consistent parameter naming (tlsproxy_client_xxx corresponds to smtp_tls_xxx). This change was made with backwards-compatible default settings. [Feature 20210926] Postfix was updated to support OpenSSL 3.0.0 API features, and to work around OpenSSL 3.0.0 bit-rot (avoid using deprecated API features). Other code health ----------------- [typos] Typo fixes by raf. [pre-release checks] Added pre-release checks to detect a) new typos in documentation and source-code comments, b) missing entries in the postfix-files file (some documentation would not be installed), c) missing rules in the postlink script (some text would not have a hyperlink in documentation), and d) missing map-based $parameter names in the proxy_read_maps default value (the proxymap daemon would not automatically authorize some proxied maps). [memory stream] Improved support for memory-based streams made it possible to inline small cidr:, pcre:, and regexp: maps in Postfix parameter values, and to eliminate some ad-hoc code that converted tlsproxy(8) protocol data to or from serialized form.