I'm also struggling with EML files. I can't open attached EML at all (Mail.app is opening).

When receiving EML files attached, no way to see them as attachments. Instead they are shown somehow inline instead of the main email body. You loose your main mail message and instead see some EML attached content inline. That is not supposed to be so. An attachment should be shown as attachment. Multiple EMLs as attachment should be also supported. That is the only reason i can't use Airmail in day-by-day business.