[cedsav]

Interesting question. Google might argue you should direct your request to those individuals you emailed to. Google storing the emails doesn't necessarily mean that they're responsible for processing your deletion request under the GDPR (or maybe it does, I'm just speculating).

[idbehold]

Google still makes available to its Gmail users the previous emails I've sent to them.

[cedsav]

Yes, but the GDPR makes a distinction between data controllers and data processors. The data controller is obligated to process your request, but Google could argue they're just the data processor, and redirect you to the users (again still speculating... not a lawyer)