(PHP 5, PHP 7, PHP 8)
iconv_mime_decode_headers — Decodes multiple MIME header fields at once
$headers, int $mode = 0, ?string $encoding = null): array|false
   Decodes multiple MIME header fields at once.
  
headersThe encoded headers, as a string.
mode
       mode determines the behaviour in the event
       iconv_mime_decode_headers() encounters a malformed
       MIME header field. You can specify any combination
       of the following bitmasks.
       
| Value | Constant | Description | 
|---|---|---|
| 1 | ICONV_MIME_DECODE_STRICT | If set, the given header is decoded in full conformance with the
            standards defined in » RFC2047.
            This option is disabled by default because there are a lot of
            broken mail user agents that don't follow the specification and don't
            produce correct MIMEheaders. | 
| 2 | ICONV_MIME_DECODE_CONTINUE_ON_ERROR | If set, iconv_mime_decode_headers() attempts to ignore any grammatical errors and continue to process a given header. | 
encoding
       The optional encoding parameter specifies the
       character set to represent the result by. If omitted or null,
       iconv.internal_encoding
       will be used.
      
   Returns an associative array that holds a whole set of
   MIME header fields specified by
   headers on success, or false
   if an error occurs during the decoding.
  
Each key of the return value represents an individual field name and the corresponding element represents a field value. If more than one field of the same name are present, iconv_mime_decode_headers() automatically incorporates them into a numerically indexed array in the order of occurrence. Note that header names are not case-insensitive.
| Version | Description | 
|---|---|
| 8.0.0 | encodingis nullable now. | 
Example #1 iconv_mime_decode_headers() example
<?php
$headers_string = <<<EOF
Subject: =?UTF-8?B?UHLDvGZ1bmcgUHLDvGZ1bmc=?=
To: example@example.com
Date: Thu, 1 Jan 1970 00:00:00 +0000
Message-Id: <example@example.com>
Received: from localhost (localhost [127.0.0.1]) by localhost
    with SMTP id example for <example@example.com>;
    Thu, 1 Jan 1970 00:00:00 +0000 (UTC)
    (envelope-from example-return-0000-example=example.com@example.com)
Received: (qmail 0 invoked by uid 65534); 1 Thu 2003 00:00:00 +0000
EOF;
$headers =  iconv_mime_decode_headers($headers_string, 0, "ISO-8859-1");
print_r($headers);
?>
The above example will output:
Array
(
    [Subject] => Prüfung Prüfung
    [To] => example@example.com
    [Date] => Thu, 1 Jan 1970 00:00:00 +0000
    [Message-Id] => <example@example.com>
    [Received] => Array
        (
            [0] => from localhost (localhost [127.0.0.1]) by localhost with SMTP id example for <example@example.com>; Thu, 1 Jan 1970 00:00:00 +0000 (UTC) (envelope-from example-return-0000-example=example.com@example.com)
            [1] => (qmail 0 invoked by uid 65534); 1 Thu 2003 00:00:00 +0000
        )
)