"on hold" - what happens with mailings
CiviCRM will not try and send to an email address that is marked on hold (regardless of any other characteristics of that email (primary, bulk mailings).

If a contact has multiple email addresses and one or more of them is on hold, then CiviMail chooses the 'next' available email address and tries to sent to that.

More background here: https://docs.civicrm.org/user/en/stable/email/maintaining-healthy-email-lists/#what-do-i-do-if-an-address-is-put-on-hold