(I thought I had filed this before, but wasn't able to find - hit me if I missed something obvious)
In our custom instance we basically do
$mailer->setSender($default_from) when $can_send_as_user and the implementation of setSender is something like $this->addHeader('List-Id', $sender); for the SendGridAdapter and $this->mailer->Sender = $sender; $this->mailer->AddCustomHeader('List-Id:' . $sender); for the php mailer lite.
If we don't do this, mailers like gmail block all incoming emails sent as users. This is the trick mailing lists use, so this will stop working once all mailing lists stop working :)
Would obviously need implementation for all mail adapters.