It's slightly scandalous how bad the Apple Contacts app is.
The test below were done in Yosemite. Maybe it's better in later OS updates but I doubt it.
Most of the time I have lists of either name and email or just email addresses.
Here's what you want for a list of just email addresses.
• In a text editor format your emails as shown below. You need a CR at the end of each line.
** Note that the mail tags in the text below are just some Apple forum stupidity I can't get rid of, just ignore them.
• Search for blank spaces and delete them
• Save as "Names.csv" or something similar
,email,
,sandy@ foo.edu,
,bill@foo.edu,
,john@foo.edu
• Open Contacts
• Contacts -> Import and find your csv file
Tick the "ignore first line" box
After import succeeds, create a new Group name in Contacts
Click Last Import in Contacts
Drag your new cards from Last Import to the group you just made
Names and email would be setup as below.
You can leave name slots blank but don't forget the commas
Search for spaces in your text editor and delete them.
firstname,lastname,email,
sandy,lake,sandy@ foo.edu,
bill,miller,bill@foo.edu,
john,smith,john@foo.edu