Zyte Smart Proxy Manager(formerly Crawlera) can process POST requests, and they're considered as a single requests, like GET requests. This is commonly used for crawling search results after filling a form.
An example for filling this form https://httpbin.org/forms/post:
curl -U CRAWLERA_APIKEY: -x proxy.crawlera.com:8010 "https://httpbin.org/post"\ -X POST -d "custname=Scrapinhub"\ -d "custtel=+55 555 5555"\ -d "custemail=no@mail.com"\ -d "size=large"\ -d "topping=bacon"\ -d "topping=cheese"\ -d "topping=onion"\ -d "delivery=13:00"\ -d "comments=hurry!"\
This response is received:
{ "args": {}, "data": "", "files": {}, "form": { "comments": "hurry!", "custemail": "no@mail.com", "custname": "Scrapinhub", "custtel": " 55 555 5555", "delivery": "13:00", "size": "large", "topping": [ "bacon", "cheese", "onion" ] }, "headers": { "Accept": "*/*", "Content-Length": "147", "Content-Type": "application/x-www-form-urlencoded", "Host": "httpbin.org", "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_3)..." }, "json": null, "origin": "123.123.123.123", "url": "https://httpbin.org/post" }