Learn Dutch: Wij verkopen elke postzegel en ieder bordspel. - We sell every postage stamp and every board game.

They are exact synonyms that both mean "every" or "each". The sentence mixes them just to provide variety and avoid repeating the same word, which is very common in Dutch.

Why does elke have an -e at the end, but ieder does not?

This happens because of noun genders. Postzegel is a de-word, so the adjective must take an -e ending, making it elke (or iedere). Bordspel is a het-word, so the adjective drops the -e when used without an article, giving us elk or ieder.

How can I easily remember the gender of compound words like postzegel and bordspel?

Compound nouns in Dutch always take the gender of their very last part. Because it is de zegel (the seal/stamp) and het spel (the game), the combined words naturally become de postzegel and het bordspel.

This lesson teaches "not anymore". How would I use that grammar to say "We don't sell board games anymore"?

To say "no longer" or "not anymore" with a general plural noun like "board games", you use geen ... meer. The sentence would become: Wij verkopen geen bordspellen meer.