I don’t know why, but Easyfind can’t find Files Contents in file type eml used by thunderbird email.

Finder show the kind as Email Message.

In my test is I rename to .txt, Easyfind work well.

The difference is that one of then has extented attibut

If file has no extended, easylink can access

You might have to add the extension .eml to the settings (see drawer).