Option for a CiviMail specific From address
This is possible insofar as we can differentiate between "singleEmail" and "flexmailer"/"civimail" in the hook_civicrm_alterMailParams()
$context
. If it's one of flexmailer or civimail then we could offer a second, CiviMail-specific From address.
Work started in https://lab.civicrm.org/extensions/sending_domain/-/tree/bulk?ref_type=heads