If you already have all the postal abbreviations memorized, the two-letter postal code system may not cause any confusion. But do all your readers have those distinctions nailed down? That’s why I’d recommend going with the AP Style for state abbreviations as part of your company’s stylebook – with exceptions.
Another consideration on why we should let go of the “words-not-numerals” rule: We use numbers a lot more these days than we did when the rules of English were created. We’re data-driven.
The AP decision to abandon the distinction apparently was a concession that people weren’t following it, so it wasn’t worth trying to enforce it. “We were swimming against the tide,” one of those responsible for the switch has said.
Now, as I try to think about weighing in on matters of grammar and writing, I try to make sure I’m not channeling Mrs. A.’s voice of “That’s not the right way of doing it.” Sometimes, the “right” way no longer makes sense, if it ever did. Other times, the old rules are solid and useful.
Almost all employees have to write emails as part of their jobs. Maybe a writer has shown an ability to write a strong email subject line. Build on that strength and show them how to write a good headline for a piece used on the company’s website.