Maya can save rendered image files in one of several standard image file formats. If you are using any of the Maya renderers; for example, Maya Software or Maya Hardware 2.0, Maya saves rendered image files in the Maya Image File Format (.iff) by default. If you are using the Arnold for Maya renderer, rendered image files are saved in the .exr format by default.
For a comprehensive list of supported file formats, see File formats.
To set the file format of rendered images
For image formats that cannot include mask or depth channels, Maya generates a separate mask or depth file.