Q:

How can I send a signed/encrypted Message with laravel? 

Laravel uses a self-written api for switfmailer.  In swiftmailer you can attach a signer with your own pem certificate and a private key:
https://swiftmailer.symfony.com/docs/messages.html#signed-encrypted-message
I would like to self sign an email, but I dont't know, how I can do that in Larvel.  Google didn't help me either. 

A:

These classes and methods are present in the vendor directory, so you are able to use it the same way in Laravel (I think this part of the code might have been taken from Symfony without any modification).