By default, all software supports multiple file extensions. Apple Mail supports at least 15 different file extensions. The basic files that Apple Mail supports are .EML. However, not all of the extensions listed on the list are always used to save the effects of work in Apple Mail. Very often, files with such extensions are used as source data files used by Apple Mail.
Apple Mail can be used to convert file formats between the file extensions listed below. You can open a file with one of the file extensions below via Apple Mail and try to save it in another file format, also supported by Apple Mail.