Decode an UTF8 email header

Question

I have an email subject of the form:

=?utf-8?B?T3.....?=

The body of the email is utf-8 base64 encoded - and has decoded fine. I am current using Perl's Email::MIME module to decode the email.

What is the meaning of the =?utf-8 delimiter and how do I extract information from this string?

Answer 1

The encoded-word tokens (as per RFC 2047) can occur in values of some headers. They are parsed as follows:

=?<charset>?<encoding>?<data>?=

Charset is UTF-8 in this case, the encoding is B which means base64 (the other option is Q which means Quoted Printable).

To read it, first decode the base64, then treat it as UTF-8 characters.

Also read the various Internet Mail RFCs for more detail, mainly RFC 2047.

Since you are using Perl, Encode::MIME::Header could be of use:

SYNOPSIS

use Encode qw/encode decode/;
$utf8   = decode('MIME-Header', $header);
$header = encode('MIME-Header', $utf8);

ABSTRACT

This module implements RFC 2047 Mime Header Encoding. There are 3 variant encoding names; MIME-Header, MIME-B and MIME-Q. The difference is described below

              decode()          encode()  
MIME-Header   Both B and Q      =?UTF-8?B?....?=  
MIME-B        B only; Q croaks  =?UTF-8?B?....?=  
MIME-Q        Q only; B croaks  =?UTF-8?Q?....?=

Answer 2

I think that the Encode module handles that with the MIME-Header encoding, so try this:

use Encode qw(decode);
my $decoded = decode("MIME-Header", $encoded);

Answer 3

Check out RFC2047. The 'B' means that the part between the last two '?'s is base64-encoded. The 'utf-8' naturally means that the decoded data should be interpreted as UTF-8.

Answer 4

MIME::Words from MIME-tools work well too for this. I ran into some issue with Encode and found MIME::Words succeeded on some strings where Encode did not.

use MIME::Words qw(:all);
$decoded = decode_mimewords(
    'To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= <keld@dkuug.dk>',
);

Answer 5

This is a standard extension for charset labeling of headers, specified in RFC2047.