What is the intended or typical use for something like this? Testing other applications that send email comes to mind, or am I missing some other uses?
A customer of mine runs a service that sends email notifications and OTP codes. We use Mailcatcher to look at the emails without having to wait for them to get to our real inboxes. Furthermore it catches all the emails, even the ones sent to somebody@example.com so we can have totally fake email addresses in our dev databases.