This is a good idea but I think you'd get more of a response if you emailed journalists from major publications as well as feminist ones. It's possible that someone will read one of these emails and try to create a story from it and the fallout from said story could affect reddit's funding and public perception negatively.

You are still fighting an uphill battle here because much of the mainstream internet sees the banning of GC and other similar subs as a "win" for women and conversely think they're the misogynistic subs and not the MRA ones. I would link all of the rape kink subs on the emails as well as MGTOW and other misogynist subs you could find. At the same time point out the banning of women spaces on reddit.

I apologize for the unsolicited advice but I think a news stories would do way better in the long run than having to laboriously email several dozen companies that may or may not advertise on reddit in the present.