Previously this test was using random email addresses in the form of
`bin2hex(random_bytes(7)) . '@example.com'`, the default address
generated by `\MailPoet\Test\DataFactories\Subscriber`. This was causing
the staff@mailpoet.com account to get banned by the MSS due to
`bad-domain-discard`s. Using the mailinator email address instead, like
the other sending tests, should prevent this from occurring.
[MAILPOET-4064]
