it's easier to do it this way imo than directly emailing them.
here's how I upload, and I think it's the quickest way. Put your image files into Google Drive and make the folder sharable to anyone. copy the Google Drive link and click on any manga series on this website. On the left hand side you will see a little flag symbol (it's used to report any issues etc.), click on that symbol and select the option about uploading and type out what series in what chapter you are sharing.
Usually mangago says "Thank you very much! :)" after they use your images (both email and report), so if someone is faking being the uploader they can take a screenshot of that message.
How do you upload chapters on this site? I've been using it for years and still have no idea. But lately, there have been people posting jokes on chapters (Like Ch 61 of Tensei Shitara Slime) and commenting that they uploaded when they didn't. So just curious how people actually do it.