Way to mask all email addresses in development environment?

Summary:

We are testing in a development environment which is not scrambled. We have set the override default address to our team's functional mailbox, but is there any other way to mask or remove all user email addresses, without having to do it manually? There are some concerns that the override could fail.

Additionally we received two identical emails for check-ins to the mailbox, but from different senders. Why could this be? (see below)

We require email notifications to be on for testing.

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