Re: [maildropl] Maildrop handling subject containing unicode characters

[Sam V. <mr...@co...>]

Milan Obuch writes:

> Hi,
>
> recently I found a problem in maildrop when handling subject containing
> unicode characters. Occasionally, I am experiencing mail not being
> delivered to some remote server with error message being (last line)
>
> 553 Unable to deliver Unicode E-mail to a non-Unicode mail server.
>
> After some investigation I found it comes from my maildrop script doing
> some kind of mailing list, and now I have a simple test case.
>
> I added to my maildrop script (another mailbox, so I can test things
> without disturbing my application) following:
>
> if (/^Subject: *(Test .*)/)
>  {Subject=$MATCH1
>   echo "subject $MATCH1"
>   xfilter 'reformail -i"Subject: $Subject"'
>  }
>
> This should just check for subject starting with Test to invoke some
> action, replacing the subject with new subject, constructed, but for
> this example it should be the same.

You can write

/^Subject:.*(<some unicode character>)/

and it'll match the subject line whether its unicode characters were  
encoded, in UTF-8 or any other encoding.

Your maildrop script can expect to see only Unicode content, and should use  
UTF-8.

> It is now understandable that mail with subject mangled this way could
> be rejected by some external mail server. Mostly it works, but this is
> just kind of happy accident, given the spec.
>
> My question is, how should this be handled correctly. If I understand
> what happens, $MATCH variable contains matched text in internal Unicode
> binary encoding, and it should be encoded back using either base64 or
> quoted printable character encoding, if some non ASCII characters are
> in string given.
>
> Any hints appreciated...

You can use reformime to reencode unicode back into ascii-only:

$ reformime -o 'Hóla!'
=?UTF-8?B?SMOzbGEh?=

So, you probably want something like:

Subject=`reformime -o "$MATCH1"`

and, with everything else, it should work.

maildrop does not do variable substitution inside backticks, so this command  
gets passed directly for execution to the shell, and it safely substitutes  
$MATCH1, from the inherited environment. 

Note that, either way, changing the subject line will likely break any  
signatures that include the original subject line.