How do I open a .eml file on my mac? Thanks!

Apple's Mail app (in Sequoia, at least) also uses the .eml format. With the free version of eM Client, I can simply drop a .eml file into the list of Inbox items and it gets added.

Mail isn't that cooperative. You have to import them. If this came as an attachment, first save it to the desktop.

From the top menu bar, choose File > Import Mailboxes…

On the palette that appears, choose the Apple Mail radio button and click Continue.

Navigate to the .eml file and select it. Click the Choose button, then Done. It will appear in the left column under the On My Mac folder. Something like this:

From what I understand, an .eml file is an email file. Double-click it and it should open with the Mail application.

In that case, right-click the file and open it with TextEdit. An .eml file is text-based. You should be able to view and extract its content.