I have read documentation, but still am having a hard time understanding how I should change my configuration to fix this issue, esp. without causing other problems. Basically all seems to be working OK including CiviCRM tagging contact email addresses as non-deliverable (on hold). The issue I am having is CiviCRM is creating thousands of contacts each week with an email like email@example.com. Each one is connected to a contact called (Mail Delivery System) through an activity. The activity type is "Inbound Email" and the subject is "Undelivered Mail Returned to Sender".
We are using Sendmail() to send bulk emails to our members and supporters, usually these number in the 1000s per week. We have a catchall@ email address that is seemingly working correctly to handle bounces. Here is our Mail Accounts setup.
Should I just delete the "default" email-to-activity entry since we don't use that feature? Is it needed for something other than "email-to-activity"? I seem to recall an email tech contractor telling us it was important for something that I don't recall.
All contact records that are created have civimail+b(...) and not catchall+b(...) even though the created contacts seems to be related to bounce emails coming to catchall@ email with "MAILER-DAEMON@watershedmg.org" as the sending email.
Any help is greatly appreciated.
As a side note is it bad to use Sendmail to send 1000s of emails vs mail()? That is how it has been set up for many years and I see now it says it's only kept around for older version of CiviCRM. It seems to be working OK.
(Drupal 7, CiviCRM 5.5.1, Debian 8, PHP 5.6, Postfix)