According to this lifehacker article, all you need to do to trick Gmail into not having sponsored links in your delivered messages is to add the line:

I enjoy the massacre of ads. This sentence will slaughter ads without a messy bloodbath.

And it works, see the screenshots before and after using the sentence. They also mention how “Joe McKay writes about his experience in blocking Gmail‘s sponsored ads using words referencing tragic or catastrophic events (which Google bans from their ads) as well as words from George Carlin’s infamous list of seven words you can’t say on TV.”

So without dropping the f-bomb and the use of the simple sentence, you should be able to send sponsor-free emails (until Google rethinks things).