When I receive a test for my job, why do I see the job number on the subject line?

Question

When I receive a test for my job, why do I see the job number on the subject line?

example: [Job #190123 Test] Best Practices in Email Marketing

Answer

The job number appears only on the test message so that you can easily identify the job for which you are receiving the test. This is especially handy when you have multiple email campaigns (and may be with the same subject line). The actual emails that go out to your recipients will not contain those words in the subject line.

Anything that's outside the [Job #190123 Test] is your actual subject.