I remember Mrs. Bishop, my third grade teacher, telling the class that we could not, under any circumstance, ever start a sentence with “and,” “but” or “so.”
Mrs. Bishop was a good teacher, but she was wrong about this. And so was everyone else’s third grade teacher.
No one seems to know how this prohibition against conjunctions began. But it’s completely incorrect.
If you need a more accepted source, check the Chicago Manual of Style. But if your boss insists that her or his third grade teacher was right no matter how much proof you provide, don’t push it.