https://bugs.exim.org/show_bug.cgi?id=2496
Bug ID: 2496
Summary: SMTPUTF8 more friendly when mail without
internationalized addresses is send using that
extension
Product: Exim
Version: 4.92
Hardware: x86
OS: All
Status: NEW
Severity: wishlist
Priority: medium
Component: Unfiled
Assignee: unallocated@???
Reporter: arekm@???
CC: exim-dev@???
Exim got SMTPUTF8 support (bug #1516) but it is not friendly enough in some
cases.
This is feature request about making it smarter and more friendly when dealing
with ascii-addressed messages but sent with SMTPUTF8 extension.
Example, SMTPUTF8 support is requested at SMTP session for message with
addresses that are pure ascii only. Client is allowed to do that.
exim relays such mail and recipients SMTP servers are required to support
SMTPUTF8 extension. That's because exim doesn't do any detection if that's
really needed and trusts smtp client.
When recipient server doesn't support SMTPUTF8 message is bounced by exim and
"utf8 support required but not offered for forwarding" is logged.
That email message with exactly the same content and headers would be delivered
just fine if only client didn't request SMTPUTF8 extension.
RFC 6531 mentions that
"An SMTPUTF8-aware SMTP client or server
that requires accurate knowledge of whether a message is
internationalized needs to parse all message header fields and MIME
header fields [RFC2045] in the message body. However, this
specification does not require that the SMTPUTF8-aware SMTP client or
server inspects the message.
"
So what could be improved is to make exim inspect messages and decide that
SMTPUTF8 isn't actually needed for particular message.
Postfix does something like that:
http://www.postfix.org/SMTPUTF8_README.html#using
"When a message is received with the SMTPUTF8 request, Postfix will deliver the
message to a non-SMTPUTF8 SMTP or LMTP server ONLY if:
* No message header value contains UTF-8.
* The envelope sender address contains no UTF-8,
* 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."
At this moment it's safer to just disable SMTPUTF8 than deal with such nasty
smtp clients ("Microsoft Navision Dynamics" in my case).
>From irc conversation it looks like doing something similar (like postfix does)
in exim means much work, so this is just a documentation of findings as a
whishlist.
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