Is it "thousands of postmen and women" or "thousands of postmen and -women"? Is the use of a hyphen correct in the latter case?
Using the hyphen would traditionally be appropriate there, though it strikes me as old-fashioned. The BBC's website, for example, regularly uses "postmen and women" without a hyphen. Of course, this is somewhat ambiguous, as it could be taken to mean the same as "thousands of women and postmen". Context usually shows what is meant, but the hyphen certainly removes all doubt.
If you wanted an alternative that avoids the hyphen problem, you could replace -women with the full word ("thousands of postmen and postwomen") or use a term that includes both categories ("thousands of postal workers", or in U.S. English "thousands of mail carriers").
Perhaps I'm being hypersensitive, but it seems to me there's something inherently sexist in constructions explicitly stating that "postal delivery workers" includes both men and women.
I know that in the UK they actually call themselves posties, but I must admit I'm intrigued by Google's definition in that link...
A mail carrier, mailman (US) or postman/postwoman (UK)
...which seems to imply either that mailman is considered "unisex", or that all American delivery staff are men.
Both versions (with and without the hyphen) are fine, meaning they both conform to common usage.
Incidentally, I assume “thousands of postmen and -women” is intended to avoid offending female postal employees. It may be well worth your time to discover whether it might have the reverse effect. This is a complex issue. See the question titled “Gender-neutral Forms”.