plugin Postie – filetype image problem with other extensions

Hi everyone. I would like to extend the publication of images via email to other extensions beyond the classic JPG, JPEG, BMP. For example, I would like to enable JFIFs. I modified WordPress so that it uploads them if I go to the media upload folder, but when they arrive from an email that manages Postie, they are not published.
I wanted to use this code {FILETYPE} The file extension (jpg, png, doc, pdf, etc) in the image configuration, but I don’t know how to write the code and I can’t find any guides about it.
Can you help me?
Thank you