Yes. Email has a "from" address that the SMTP protocol (the thing that often carries emails) that is separate from the IP address of the sending server, the ex

Yes. Email has a "from" address that the SMTP protocol (the thing that often carries emails) that is separate from the IP address of the sending server, the exact same way "CALLER-ID" is a separate field from the billing address (called ANI, or Automatic Network Identification) in telephone networks. Requiring that ANI match CALLER-ID would break many voicemail systems and call-forwarding systems. They can be fixed, but it will be expensive to do so. Similarly, requiring the email "from" address agree with the SMTP server's responsibilities breaks mailing lists and email-forwarding, and again, this can be fixed, but it is proving expensive to do so.