I would like to use plain email senders for our setup.

1. Default email sender (settings) does not allow to set plain email text, only named email (e.g. Example <mail@example.org> but not mail@example.org).
2. Setting mail@example.org <mail@example.org> will fail to send emails because of smtp server error "expected one email sender".

In a campaign you can set mail@example.org, however the email client will show it as <mail@example.org> instead of a plain email address.