When messages are dragged from a Eudora mailbox window, a single file is created with full message headers (rather than a separate file for each email). Another useless ".toc" file is created too but that is easily ignored.

Within that single text file, each mail message -- without exception -- is prefaced by this very peculiar tag:
From ???@???

In other words, the word "From" then a space, then three question marks, an @ symbol, and then another three question marks. Nothing else appears on that line (i.e., no colons or other punctuation). After that, the regular email appears with the real "From" line a few lines down, etc.

I hope this helps, Jeff!