It would only be at all valid if it was forwarded to employees who weren’t in a customer facing role.

Saying that you’re required to give a content warning to an account manager for material related to your business relationship puts the burden of responsibility onto the victim. Dealing with the psychological impact is the responsibility of their employer, not the customer.

No, even in a customer-facing role, you won't have to put up with every s**. I mean, it's a business for electronics, not a porn-shop or moderation for explicit material at some social media-platform. There should be a line on what they have to tolerate.

And the test is “did it come from my employer to a customer I am responsible for?”

From the little we know the "material" in question would be photoshops made to harass Limor, made by someone at sparkfun. So it would be weird for sparkfun to complain , given the content originated with one of their employees. (Allegedly)