If you did not migrate your account yet, visit https://idp-portal-info.suse.com/
Any email sent to the @opensuse.org email address will be redirected to your normal account and not stored anywhere in the openSUSE infrastructure. So, to receive email with your @opensuse.org you have nothing to do. Just check that those emails do not end in your spam folder since they are using a different address.
To send email using your @opensuse.org email address, configure in your mail program a new identity using this email address and send email the same way as with your already existing account. There is no opensuse.org mail server that you can use.
In case you have some issues, need to change where email is forwarded, etc. please contact admin(at)opensuse.org