Create a simple email listing

Create a simple email listing

I've spent the entire day attempting and researching how I can create a simple email list.  I need to send regular emails out to 2 different groups of people and would like to create listing for each.  Too timely to drag each name into the TO field with each email.   At the present, I've created a group called "MA Board" and was able to only add @seatrailma.com (our domain) email addresses.  It will not allow me to add any other types of email accounts.  Please help!
Thanks, Candy