.eml vs INBOX file

When I select an email in Apple Mail and press F1 sometimes it is sent to EagleFiler as a .eml file and sometimes as an INBOX file. I cannot figure out why F1 imports as either an .eml or INBOX file. There seems to be no pattern for the different import file formats. How can I always import my emails from Apple Mail into EagleFiler as a .eml file?

By default, EagleFiler imports a single selected message as a .eml message file and multiple selected messages as a mailbox file. Please see Importing Mail and Importing Mail From Apple Mail for more information and options.