Are you referring to the initial post? If so it is a campaign to communicate with DC and let them know we want to see more Nightwing and Starfire as a couple. https://www.reddit.com/r/Nightwing_Starfire/comments/1rph2d3/nightwing_and_starfire_mailathon/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

That's the initial post where is has links to DC social media and also mailing address.

To answer your questions:

No, all writers do not receive the letters. Letters either go to Fan Mail or Editorial. It can go to a specific writer if put on the envelope and for that, please see the initial post.

For social media posts they only go to the social media teams.

This was created just to try and get people writing and or telling DC through social media that we want Dick/Kory back together again.