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diff --git a/README_FILES/SMTPUTF8_README b/README_FILES/SMTPUTF8_README new file mode 100644 index 0000000..5496a3b --- /dev/null +++ b/README_FILES/SMTPUTF8_README @@ -0,0 +1,294 @@ + PPoossttffiixx SSMMTTPPUUTTFF88 ssuuppppoorrtt + +------------------------------------------------------------------------------- + +OOvveerrvviieeww + +This document describes Postfix support for Email Address Internationalization +(EAI) as defined in RFC 6531 (SMTPUTF8 extension), RFC 6532 (Internationalized +email headers) and RFC 6533 (Internationalized delivery status notifications). +Introduced with Postfix version 3.0, this fully supports UTF-8 email addresses +and UTF-8 message header values. + +Topics covered in this document: + + * Building with/without SMTPUTF8 support + * Enabling Postfix SMTPUTF8 support + * Using Postfix SMTPUTF8 support + * SMTPUTF8 autodetection + * Limitations of the current implementation + * Compatibility with pre-SMTPUTF8 environments + * Compatibility with IDNA2003 + * Credits + +BBuuiillddiinngg PPoossttffiixx wwiitthh//wwiitthhoouutt SSMMTTPPUUTTFF88 ssuuppppoorrtt + +Postfix will build with SMTPUTF8 support if the ICU version >= 46 library and +header files are installed on the system. The package name varies with the OS +distribution. The table shows package names for a number of platforms at the +time this text was written. + + _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ + |OOSS DDiissttrriibbuuttiioonn |PPaacckkaaggee | + |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _ | + |FreeBSD, NetBSD, etc.|icu | + |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _ | + |Centos, Fedora, RHEL |libicu-devel| + |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _ | + |Debian, Ubuntu |libicu-dev | + |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _ | + +To force Postfix to build without SMTPUTF8, specify: + + $ mmaakkee mmaakkeeffiilleess CCCCAARRGGSS==""--DDNNOO__EEAAII ......"" + +See the INSTALL document for more "make makefiles" options. + +EEnnaabblliinngg PPoossttffiixx SSMMTTPPUUTTFF88 ssuuppppoorrtt + +There is more to SMTPUTF8 than just Postfix itself. The rest of your email +infrastructure also needs to be able to handle UTF-8 email addresses and +message header values. This includes SMTPUTF8 protocol support in SMTP-based +content filters (Amavisd), LMTP servers (Dovecot), and down-stream SMTP +servers. + +Postfix SMTPUTF8 support is enabled by default, but it may be disabled as part +of a backwards-compatibility safety net (see the COMPATIBILITY_README file). + +SMTPUTF8 support is enabled by setting the smtputf8_enable parameter in +main.cf: + + # ppoossttccoonnff ""ssmmttppuuttff88__eennaabbllee == yyeess"" + # ppoossttffiixx rreellooaadd + +(With Postfix <= 3.1, you may also need to specify "ooppttiioonn__ggrroouupp == cclliieenntt" in +Postfix MySQL client files, to enable UTF8 support in MySQL queries. This +setting is the default as of Postfix 3.2.) + +With SMTPUTF8 support enabled, Postfix changes behavior with respect to earlier +Postfix releases: + + * UTF-8 is permitted in the myorigin parameter value. However, the myhostname + and mydomain parameters must currently specify ASCII-only domain names. + This limitation may be removed later. + + * UTF-8 is the only form of non-ASCII text that Postfix supports in access + tables, address rewriting tables, and other tables that are indexed with an + email address, hostname, or domain name. + + * The header_checks-like and body_checks-like features are not UTF-8 enabled, + and therefore they do not enforce UTF-8 syntax rules on inputs and outputs. + The reason is that non-ASCII text may be sent in encodings other than UTF- + 8, and that real email sometimes contains malformed headers. Instead of + skipping non-UTF-8 content, Postfix should be able to filter it. You may + try to enable UTF-8 processing by starting a PCRE pattern with the sequence + (*UTF8), but this is will result in "message not accepted, try again later" + errors when the PCRE pattern matcher encounters non-UTF-8 input. Other + features that are not UTF-8 enabled are smtpd_command_filter, + smtp_reply_filter, the *_delivery_status_filter features, and the + *_dns_reply_filter features (the latter because DNS is by definition an + ASCII protocol). + + * The Postfix SMTP server announces SMTPUTF8 support in the EHLO response. + + 220 server.example.com ESMTP Postfix + EEHHLLOO cclliieenntt..eexxaammppllee..ccoomm + 250-server.example.com + 250-PIPELINING + 250-SIZE 10240000 + 250-VRFY + 250-ETRN + 250-STARTTLS + 250-AUTH PLAIN LOGIN + 250-ENHANCEDSTATUSCODES + 250-8BITMIME + 250-DSN + 250 SMTPUTF8 + + * The Postfix SMTP server accepts the SMTPUTF8 request in MAIL FROM and VRFY + commands. + + MMAAIILL FFRROOMM::<<aaddddrreessss>> SSMMTTPPUUTTFF88 ...... + + VVRRFFYY aaddddrreessss SSMMTTPPUUTTFF88 + + * The Postfix SMTP client may issue the SMTPUTF8 request in MAIL FROM + commands. + + * The Postfix SMTP server accepts UTF-8 in email address domains, but only + after the remote SMTP client issues the SMTPUTF8 request in MAIL FROM or + VRFY commands. + +Postfix already permitted UTF-8 in message header values and in address +localparts. This does not change. + +UUssiinngg PPoossttffiixx SSMMTTPPUUTTFF88 ssuuppppoorrtt + +After Postfix SMTPUTF8 support is turned on, Postfix behavior will depend on 1) +whether a remote SMTP client requests SMTPUTF8 support, 2) the presence of UTF- +8 content in the message envelope and headers, and 3) whether a down-stream +SMTP (or LMTP) server announces SMTPUTF8 support. + + * When the Postfix SMTP server receives a message WITHOUT the SMTPUTF8 + request, Postfix handles the message as it has always done (at least that + is the default, see autodetection below). Specifically, the Postfix SMTP + server does not accept UTF-8 in the envelope sender domain name or envelope + recipient domain name, and the Postfix SMTP client does not issue the + SMTPUTF8 request when delivering that message to an SMTP or LMTP server + that announces SMTPUTF8 support (again, that is the default). Postfix will + accept UTF-8 in message header values and in the localpart of envelope + sender and recipient addresses, because it has always done that. + + * When the Postfix SMTP server receives a message WITH the SMTPUTF8 request, + Postfix will issue the SMTPUTF8 request when delivering that message to an + SMTP or LMTP server that announces SMTPUTF8 support. This is not + configurable. + + * When a message is received with the SMTPUTF8 request, Postfix will deliver + the message to a non-SMTPUTF8 SMTP or LMTP server ONLY if: + + o No message header value contains UTF-8. + + o The envelope sender address contains no UTF-8, + + o No envelope recipient address for that specific SMTP/LMTP delivery + transaction contains UTF-8. + + NOTE: Recipients in other email delivery transactions for that same + message may still contain UTF-8. + + Otherwise, Postfix will return the recipient(s) for that email delivery + transaction as undeliverable. The delivery status notification message will + be an SMTPUTF8 message. It will therefore be subject to the same + restrictions as email that is received with the SMTPUTF8 request. + + * When the Postfix SMTP server receives a message with the SMTPUTF8 request, + that request also applies after the message is forwarded via a virtual or + local alias, or $HOME/.forward file. + +SSMMTTPPUUTTFF88 aauuttooddeetteeccttiioonn + +This section applies only to systems that have SMTPUTF8 support turned on +(smtputf8_enable = yes). + +For compatibility with pre-SMTPUTF8 environments, Postfix does not +automatically set the "SMTPUTF8 requested" flag on messages from non-SMTPUTF8 +clients that contain an UTF-8 header value or UTF-8 address localpart. This +would make such messages undeliverable to non-SMTPUTF8 servers, and could be a +barrier to SMTPUTF8 adoption. + +By default, Postfix sets the "SMTPUTF8 requested" flag only on address +verification probes and on Postfix sendmail submissions that contain UTF-8 in +the sender address, UTF-8 in a recipient address, or UTF-8 in a message header +value. + + /etc/postfix/main.cf: + smtputf8_autodetect_classes = sendmail, verify + +However, if you have a non-ASCII myorigin or mydomain setting, or if you have a +configuration that introduces UTF-8 addresses with virtual aliases, canonical +mappings, or BCC mappings, then you may have to apply SMTPUTF8 autodetection to +all email: + + /etc/postfix/main.cf: + smtputf8_autodetect_classes = all + +This will, of course, also flag email that was received without SMTPUTF8 +request, but that contains UTF-8 in a sender address localpart, receiver +address localpart, or message header value. Such email was not standards- +compliant, but Postfix would have delivered it if SMTPUTF8 support was +disabled. + +LLiimmiittaattiioonnss ooff tthhee ccuurrrreenntt iimmpplleemmeennttaattiioonn + +The Postfix implementation is a work in progress; limitations are steadily +being removed. The text below describes the situation at one point in time. + +NNoo aauuttoommaattiicc ccoonnvveerrssiioonnss bbeettwweeeenn AASSCCIIII aanndd UUTTFF--88 ddoommaaiinn nnaammeess.. + +Some background: According to RFC 6530 and related documents, an +internationalized domain name can appear in two forms: the UTF-8 form, and the +ASCII (xn--mumble) form. An internationalized address localpart must be encoded +in UTF-8; the RFCs do not define an ASCII alternative form. + +Postfix currently does not convert internationalized domain names from UTF- +8 into ASCII (or from ASCII into UTF-8) before using domain names in SMTP +commands and responses, before looking up domain names in lists such as +mydestination, relay_domains or in lookup tables such as access tables, etc., +before using domain names in a policy daemon or Milter request, or before +logging events. + +Postfix does, however, casefold domain names and email addresses before +matching them against a Postfix configuration parameter or lookup table. + +In order to use Postfix SMTPUTF8 support: + + * The Postfix parameters myhostname and mydomain must be in ASCII form. One + is a substring of the other, and the myhostname value is used in SMTP + commands and responses that require ASCII. The parameter myorigin (added to + local addresses without domain) supports UTF-8. + + * You need to configure both the ASCII and UTF-8 forms of an + Internationalized domain name in Postfix parameters such as mydestination + and relay_domains, as well as lookup table search keys. + + * Milters, content filters, policy servers and logfile analysis tools need to + be able to handle both the ASCII and UTF-8 forms of Internationalized + domain names. + +CCoommppaattiibbiilliittyy wwiitthh pprree--SSMMTTPPUUTTFF88 eennvviirroonnmmeennttss + +MMaaiilliinngg lliissttss wwiitthh UUTTFF--88 aanndd nnoonn--UUTTFF--88 ssuubbssccrriibbeerrss + +With Postfix, there is no need to split mailing lists into UTF-8 and non-UTF- +8 members. Postfix will try to deliver the non-UTF8 subscribers over +"traditional" non-SMTPUTF8 sessions, as long as the message has an ASCII +envelope sender address and all-ASCII header values. The mailing list manager +may have to apply RFC 2047 encoding to satisfy that last condition. + +PPrree--eexxiissttiinngg nnoonn--AASSCCIIII eemmaaiill fflloowwss + +With "smtputf8_enable = no", Postfix handles email with non-ASCII in address +localparts (and in headers) as before. The vast majority of email software is +perfectly capable of handling such email, even if pre-SMTPUTF8 standards do not +support such practice. + +RReejjeeccttiinngg nnoonn--UUTTFF88 aaddddrreesssseess + +With "smtputf8_enable = yes", Postfix requires that non-ASCII address +information is encoded in UTF-8 and will reject other encodings such as ISO- +8859. It is not practical for Postfix to support multiple encodings at the same +time. There is no problem with RFC 2047 encodings such as "=?ISO-8859- +1?Q?text?=", because those use only characters from the ASCII characterset. + +RReejjeeccttiinngg nnoonn--AASSCCIIII aaddddrreesssseess iinn nnoonn--SSMMTTPPUUTTFF88 ttrraannssaaccttiioonnss + +Setting "strict_smtputf8 = yes" in addition to "smtputf8_enable = yes" will +enable stricter enforcement of the SMTPUTF8 protocol. Specifically, the Postfix +SMTP server will not only reject non-UTF8 sender or recipient addresses, it +will in addition accept UTF-8 sender or recipient addresses only when the +client requests an SMTPUTF8 mail transaction. + +CCoommppaattiibbiilliittyy wwiitthh IIDDNNAA22000033 + +Postfix >= 3.2 by default disables the 'transitional' compatibility between +IDNA2003 and IDNA2008, when converting UTF-8 domain names to/from the ASCII +form that is used in DNS lookups. This makes Postfix behavior consistent with +current versions of the Firefox and Chrome web browsers. Specify +"enable_idna2003_compatibility = yes" to get the historical behavior. + +This affects the conversion of domain names that contain for example the German +sz (ß) and the Greek zeta (ς). See http://unicode.org/cldr/utility/idna.jsp +for more examples. + +CCrreeddiittss + + * May 15, 2014: Arnt Gulbrandsen posted his patch for Unicode email support. + This work was sponsored by CNNIC. + + * July 15, 2014: Wietse integrated Arnt Gulbrandsen's code and released + Postfix with SMTPUTF8 support. + + * January 2015: Wietse added UTF-8 support for casefolding in Postfix lookup + tables and caseless string comparison in Postfix list-based features. + |