Where must finisher files (for powermail finisher) be located? - typo3

Question

I am currently trying to add a finisher to my powerplay form.
The target is to delete all elements in a specific folder after the form is submited.
I currently use :
this tutorial
I first put this into my setup.txt
plugin.tx_powermail.settings.setup {
finishers {
1 {
class = Vendor\Ext\Finisher\DoSomethingFinisher
}
}
}
at this location: ftp://ftpIP/typo3cms/pagename/typo3conf/ext/powermail/Configuration/TypoScript/Main/setup.txt
Now i should create a PHP-File:
Add a php-file DoSomethingFinisher.php and extend your class with the AbstractFinisher from powermail:
But where shuld I place that PHP File? In the same place as the setup.txt?
Hope someone can help. Thank you very much.
Thomas

Answer 1

That question is related to TYPO3 autoloading and not to powermail. If you want to add PHP-Files to your TYPO3, you should use an extension.
There are some manuals how to get the autoloading to work with your PHP-Files (see https://docs.typo3.org/typo3cms/CoreApiReference/ApiOverview/Autoloading/Index.html).

Answer 2

You shouldn't modify the files in the folder powermail, otherwise you will be in trouble when you want to update the extension. Instead, create a new extension with extension_builder or take powermailextended and modify that extension.
Assuming you use powermailextended:
If you call the Finisher In2code\Powermailextended\Finisher\MyFinisher, then it needs to go in EXT:powermailextend\Classes\Finisher\MyFinisher - this is how Typo3 autoloads the PHP files.