301033Postfix SMTPUTF8 support (unicode email addresses)
- Jul 15, 2014Proudly presenting Postfix SMTPUTF8 support! Below is text from
the RELEASE_NOTES file for postfix-2.12-20140715, to be uploaded
Major changes with snapshot 20140715
Support for Internationalized Email, also known as EAI or SMTPUTF8,
defined in RFC 6530..6533. This supports UTF8 in SMTP/LMTP sender
addresses, recipient addresses, and message header values. The
implementation is based on initial work by Arnt Gulbrandsen that
was funded by CNNIC.
This text describes:
- Compatibility with pre-SMTPUTF8 environments,
- How to enable SMTPUTF8 support,
- How to use SMTPUTF8 support,
- SMTPUTF8 autodetection,
- Limitations of the current implementation.
Compatibility with pre-SMTPUTF8 environments
Mailing list friendliness
In the future, mailing lists will have a mix of UTF8 and non-UTF8
subscribers. With Postfix, there is no need to split the lists
into UTF8 and non-UTF8 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 the second condition).
Pre-existing non-ASCII mail flows
In pre-SMTPUTF8 environments, mail with UTF8 in address localparts
(and in headers) works just fine because the vast majority of mail
software including Postfix is perfectly capable of handling such
mail, even if pre-SMTPUTF8 standards do not support this.
Therefore, when Postfix SMTPUTF8 support is turned on, Postfix must
not suddenly start to break pre-existing mail flows with UTF8 in
addres localparts (and in headers).
Thus, Postfix continues to permit UTF8 in address localparts (and
in headers) in mail from and to pre-SMTPUTF8 systems. At least,
that is the default.
Enabling Postfix SMTPUTF8 support
By default, SMTPUTF8 support is disabled, and Postfix should work
exactly as it has worked before.
SMTPUTF8 support is enabled by setting in main.cf:
smtputf8_enable = yes
and by issuing the "postfix reload" command.
With SMTPUTF8 support enabled, Postfix changes behavior as follows:
- The Postfix SMTP server announces SMTPUTF8 support in the EHLO
250-AUTH PLAIN LOGIN
- The Postfix SMTP server accepts the SMTPUTF8 request in MAIL FROM
and VRFY commands.
MAIL FROM:<address> SMTPUTF8
VRFY address SMTPUTF8
- The Postfix SMTP client may issue the SMTPUTF8 request in MAIL FROM
- UTF8 is supported anywhere in an email address, not just silently
permitted in the localpart, but only after the client issues MAIL
FROM or VRFY as shown above.
- UTF8 was already silently permitted in message header values.
SMTP-based content filters (Amavisd) and LMTP servers (Dovecot)
will need to be updated to support SMTPUTF8. A notice has been
sent to the respective maintainers.
Using Postfix 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 UTF8 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 an SMTP or LMTP server that announces
SMTPUTF8 support (again, that is the default).
- 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 server ONLY if:
- No message header value contains UTF8.
- The envelope sender address contains no UTF8,
- No envelope recipient address for that specific SMTP/LMTP
delivery transaction contains UTF8.
NOTE: Recipients in other mail delivery transactions for
that same message may still contain UTF8.
Otherwise, Postfix will return the recipient(s) for that mail
delivery transaction as undeliverable. The delivery status
notification message will be subject to the same restrictions
as mail 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.
By default, Postfix sets the "SMTPUTF8 requested" bit on address
verification probes and on Postfix sendmail submissions that contain
UTF8 in the sender address, UTF8 in a recipient address, or UTF8
in a message header value.
smtputf8_autodetect_classes = sendmail, verify
This will suffice for the vast majority of sites. It minimizes the
chances of accidentally setting the "SMTPUTF8 requested" bit on a
message from a non-SMTPUTF8 client, thereby making that message
undeliverable to a non-SMTPUTF8 server as discussed above. Remember,
once a message is flagged as "SMTPUTF8 requested", the Postfix SMTP
client may not be able to deliver it to a non-SMTPUTF8 server.
However, if you have a non-ASCII myorigin or mydomain setting, or
if you have virtual aliases, canonical mappings, or BCC mappings
that introduce UTF8 addresses, then you may have to apply SMTPUTF8
autodetection to all mail:
smtputf8_autodetect_classes = all
This will, of course, also flag mail that was received without
SMTPUTF8 request, but that contains UTF8 in a sender address
localpart, receiver address localpart, or message header value.
Such mail was not standards-compliant, but Postfix would have
delivered it if SMTPUTF8 support was disabled.
Limitations of Postfix SMTPUTF8 support
"Internationalized" domain names can appear in two forms: the UTF8
form, and the ASCII (xn--mumble) form.
No characterset canonicalization for non-ASCII domain names.
Postfix currently does not translate domain names from UTF8 into
ASCII (or ASCII into UTF8) before looking up the domain name in
mydestination, relay_domains, access tables, etc., before logging
the domain name, or before using the domain name in a policy daemon
or Milter request. You will have to configure both UTF8 and ASCII
forms in Postfix configuration files; and both forms will have to
be handled by logfile tools, policy daemons and Milters.
No case canonicalization for non-ASCII characters.
Postfix currently does not case-fold non-ASCII characters when
looking up an "Internationalized" domain name in mydestination,
relay_domains, access maps, etc. Some non-ASCII scripts do not
distinguish between upper and lower case, some have different numbers
of upper and lower case characters, and reportedly some even have
title case in addition to upper and lower case (at this time it
is unclear if those will ever be used in email addresses, though).