According to the docs, AWS SES has some requirements on what is an allowable MAIL FROM domain:
The subdomain you use for your MAIL FROM domain has to meet the following requirements:
The MAIL FROM domain has to be a subdomain of the verified identity (email address or domain) that you send email from. For example, mail.example.com is a valid MAIL FROM domain for the domain example.com.
The MAIL FROM domain shouldn't be a domain that you send email from. If you have to use the MAIL FROM domain in a From address, either disable email feedback forwarding and receive your bounces through Amazon SNS notifications, or ensure that your MAIL FROM domain is not the destination for feedback forwarding. To determine the destination of email forwarding feedback, see Email feedback forwarding destination.
The MAIL FROM domain shouldn't be a domain that you use to receive email.
What is the reason for these requirements? Is this a general rule for all email services or just an AWS SES thing? In particular, I currently have my DNS SPF/DKIM/DMARC records set up so that I can send from both AWS SES and Google Workspace (formerly G Suite). For example, my current outbound emails from Google Workspace would have a "MAIL FROM" header of admin@mydomain.com which is the identical value for the "From" header. Does this cause problems?