CiviMail silently ignore an obviously wrong email account (the default)

Hi,

Just realised that I forgot to configure the mail account on one of our civi, so it was happily sending with a bogus NOREPLY email bounce.

I want to configure the cronjob so when/if there is the default mail account or if they aren't any
1) I display a warning message
2) I use the email of the sender (from)

Plan B if you prefer:
1) I display an error message and die()