diff options
Diffstat (limited to '')
| -rw-r--r-- | proto/SMTPUTF8_README.html | 399 |
1 files changed, 399 insertions, 0 deletions
diff --git a/proto/SMTPUTF8_README.html b/proto/SMTPUTF8_README.html new file mode 100644 index 0000000..9389297 --- /dev/null +++ b/proto/SMTPUTF8_README.html @@ -0,0 +1,399 @@ +<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN" + "http://www.w3.org/TR/html4/loose.dtd"> + +<html> + +<head> + +<title>Postfix SMTPUTF8 support</title> + +<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> + +</head> + +<body> + +<h1><img src="postfix-logo.jpg" width="203" height="98" ALT=""> +Postfix SMTPUTF8 support +</h1> + +<hr> + +<h2> Overview </h2> + +<p> 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. </p> + +<p> Topics covered in this document: </p> + +<ul> + +<li><a href="#building">Building with/without SMTPUTF8 support</a> + +<li><a href="#enabling">Enabling Postfix SMTPUTF8 support</a> + +<li><a href="#using">Using Postfix SMTPUTF8 support</a> + +<li><a href="#detecting">SMTPUTF8 autodetection</a> + +<li><a href="#limitations">Limitations of the current implementation</a> + +<li><a href="#compatibility">Compatibility with pre-SMTPUTF8 environments</a> + +<li><a href="#idna2003">Compatibility with IDNA2003</a> + +<li><a href="#credits">Credits</a> + +</ul> + +<h2> <a name="building">Building Postfix with/without SMTPUTF8 support</a> </h2> + +<p> 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. +</p> + +<blockquote> + +<table border="1"> + +<tr> <th> OS Distribution </th> <th> Package </th> </tr> + +<tr> <td> FreeBSD, NetBSD, etc. </td> <td> icu </td> </tr> + +<tr> <td> Centos, Fedora, RHEL </td> <td> libicu-devel </td> </tr> + +<tr> <td> Debian, Ubuntu </td> <td> libicu-dev </td> </tr> + +</table> + +</blockquote> + +<p> To force Postfix to build without SMTPUTF8, specify: </p> + +<blockquote> +<pre> +$ <b>make makefiles CCARGS="-DNO_EAI ..."</b> +</pre> +</blockquote> + +<p> See the INSTALL document for more "make makefiles" options. </p> + +<h2> <a name="enabling">Enabling Postfix SMTPUTF8 support</a> </h2> + +<p> 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. </p> + +<p> 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). </p> + +<p> SMTPUTF8 support is enabled by setting the smtputf8_enable +parameter in main.cf:</p> + +<blockquote> +<pre> +# <b>postconf "smtputf8_enable = yes"</b> +# <b>postfix reload</b> +</pre> +</blockquote> + +<p> (With Postfix ≤ 3.1, you may also need to specify "<b>option_group += client</b>" in Postfix MySQL client files, to enable UTF8 support +in MySQL queries. This setting is the default as of Postfix 3.2.) </p> + +<p> With SMTPUTF8 support enabled, Postfix changes behavior with +respect to earlier Postfix releases: </p> + +<ul> + +<li> <p> 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. </p> + +<li> <p> 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. </p> + +<li> <p> 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). </p> + +<li> <p> The Postfix SMTP server announces SMTPUTF8 support in the +EHLO response. </p> + +<pre> +220 server.example.com ESMTP Postfix +<b>EHLO client.example.com</b> +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 +</pre> + +<li> <p> The Postfix SMTP server accepts the SMTPUTF8 request in +MAIL FROM and VRFY commands. </p> + +<pre> +<b>MAIL FROM:<address> SMTPUTF8 ...</b> + +<b>VRFY address SMTPUTF8</b> +</pre> + +<li> <p> The Postfix SMTP client may issue the SMTPUTF8 request in +MAIL FROM commands. </p> + +<li> <p> 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. </p> + +</ul> + +<p> Postfix already permitted UTF-8 in message header values +and in address localparts. This does not change. </p> + +<h2> <a name="using">Using Postfix SMTPUTF8 support</a> </h2> + +<p> 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. </p> + +<ul> + +<li> <p> 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. +</p> + +<li> <p> 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. </p> + +<li> <p> When a message is received with the SMTPUTF8 request, +Postfix will deliver the message to a non-SMTPUTF8 SMTP or LMTP +server ONLY if: </p> + + <ul> + + <li> <p> No message header value contains UTF-8. </p> + + <li> <p> The envelope sender address contains no UTF-8, </p> + + <li> <p> No envelope recipient address for that specific + SMTP/LMTP delivery transaction contains UTF-8. </p> + + <blockquote> <p> NOTE: Recipients in other email delivery + transactions for that same message may still contain UTF-8. + </p> </blockquote> + + </ul> + + <p> 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. </p> + +<li> <p> 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. +</p> + +</ul> + +<h2> <a name="detecting">SMTPUTF8 autodetection</a> </h2> + +<p> This section applies only to systems that have SMTPUTF8 support +turned on (smtputf8_enable = yes). </p> + +<p> 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. +</p> + +<p> 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. </p> + +<blockquote> +<pre> +/etc/postfix/main.cf: + smtputf8_autodetect_classes = sendmail, verify +</pre> +</blockquote> + +<p> 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: </p> + +<blockquote> +<pre> +/etc/postfix/main.cf: + smtputf8_autodetect_classes = all +</pre> +</blockquote> + +<p> 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. </p> + +<h2> <a name="limitations">Limitations of the current implementation</a> +</h2> + +<p> The Postfix implementation is a work in progress; limitations +are steadily being removed. The text below describes the situation +at one point in time. </p> + +<h3> No automatic conversions between ASCII and UTF-8 domain names. </h3> + +<p> 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. </p> + +<p> 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. +</p> + +<p> Postfix does, however, casefold domain names and email addresses +before matching them against a Postfix configuration parameter or +lookup table. </p> + +<p> In order to use Postfix SMTPUTF8 support: </p> + +<ul> + +<li> <p> 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. </p> + +<li> <p> 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. </p> + +<li> <p> 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. </p> + +</ul> + +<h2> <a name="compatibility">Compatibility with pre-SMTPUTF8 +environments</a> </h2> + +<h3> Mailing lists with UTF-8 and non-UTF-8 subscribers </h3> + +<p> 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. </p> + +<h3> Pre-existing non-ASCII email flows </h3> + +<p> 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. </p> + +<h3> Rejecting non-UTF8 addresses </h3> + +<p> 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. </p> + +<h3> Rejecting non-ASCII addresses in non-SMTPUTF8 transactions </h3> + +<p> 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. </p> + +<h2> <a name="idna2003">Compatibility with IDNA2003</a> </h2> + +<p> 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. </p> + +<p> 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. </p> + +<h2> <a name="credits">Credits</a> </h2> + +<ul> + +<li> <p> May 15, 2014: Arnt Gulbrandsen posted his patch for Unicode +email support. This work was sponsored by CNNIC. </p> + +<li> <p> July 15, 2014: Wietse integrated Arnt Gulbrandsen's code +and released Postfix with SMTPUTF8 support. </p> + +<li> <p> January 2015: Wietse added UTF-8 support for casefolding +in Postfix lookup tables and caseless string comparison in Postfix +list-based features. </p> + +</ul> + +</body> + +</html> + |