Getting a Text from someone that does not have my mobile number but has my email
Hello Mario and welcome to Ask Different community. Yes, this is possible and you may have it configured from Settings to receive SMS through your email. As pointed in this related question cant get my number to change from email to my phone number


  Messages is NOT sending a message via email. It is simply using the email (which is likely your Apple ID), as an identifier of your device. This lets other Apple users send you a message to either your phone number or email address. This is useful on iPads, iPod Touch, and Macs, who can not send to phone numbers, because they do not have phone service. So, with Messages on your iPhone, someone on their Mac can send you a message, and you can message back!