bug#21733: 25.0.50; Umlaut in address makes smtpmail-via-smtp fail

[Stephen Berman <stephen.berman@gmx.net>]

On Thu, 22 Oct 2015 10:00:34 -0400 Random832 <random832@fastmail.com> wrote:

> Stephen Berman <stephen.berman@gmx.net> writes:
>> I tried to send an email with Gnus to an address containing an umlaut
>> ('ä') in the domain name, and it failed with the error "Sending failed:
>> 501 Syntax error in parameters or arguments".  When I tried sending the
>> same email to the same address using the GMX webmail interface, it
>> succeeded.  A copy of the sent email showed an address containing only
>> ascii characters instead of the address with the umlaut, so I assume the
>> latter is aliased to the former and GMX automatically found this.
>
> Did this address begin with "xn--" in the segment which had contained
> non-ascii characters in the original, such as "xn--nt-via" for "nät"?

Yes, indeed!

>> It
>> would be nice if smtpmail.el could do the same thing instead of erroring
>> out.  I can reproduce the same error using the fake address
>> <stephen.berman@gmx.nät> (backtrace attached).
>
> There is a file called punycode.el in libidn which encodes strings in
> the way I mentioned above, maybe it would be worthwhile to include this
> in Emacs - or at least have a hook which will use it if possible and
> error out immediately (for domains containing non-ASCII characters) if
> it's not present. This would be relevant to more places than just email.
>
> This uses a command-line tool (part of libidn) to do the actual
> decoding, I don't know how feasible it would be to do it in pure elisp.

Very interesting, thanks for pointing this out!  I hope something like
this can be added to Emacs.

Steve Berman