Fix header encoding detection problems

[stefanullrich]

Pull Request

Description

This will fix a problem with the header encoding detection on specific mails.

Fixes #595

Problem

While listing the content of a specific folder with something like

$messages = $folder->messages()->all()->get();

We are receiving an ErrorException:

Uninitialized string offset 0

which is based on the composer autoload feature.

This error occurs, if there is a mail within the folder (mainly spam messages) containing the following From-header:

...
Message-ID: <xxx_replaced_xxx@mail.gmail.com>
From: "\"High-Speed-Deal\" ." <info@spam.domain.invalid>
Date: Wed, 28 Aug 2025 12:31:41 +0000
...

If such a mail is parsed, the following string ('\\') is passed to the getEncoding function in HeaderDecoder.php and then in line 68:

if (property_exists('\\', 'parameters')) {

This will cause composer to try to autoload the "class" and then the exception is thrown.

Solution

To prevent the autoloading, a check is performed to see whether $structure is an object. If all conditions within the getEncoding() method fail, the fallback encoding is returned.

[stefanullrich]

Hello @Webklex,
Is there a way to merge this, or is something unclear?