It happened to me recently. It’s the spam filter policies of the big providers. Using Amazon SES - Mail Landing In Spam Folder - #8 by maximiliank
I’ve seen people say Gmail/google also referred them back to SES. SES won’t do anything besides sell you a dedicated IP. I’m not sure how often they allow you to change that IP. Either way, changing the IP isn’t a solution.
There needs to be a protest regarding the spam filter policies of gmail, yahoo, and outlook.