Yes, you can import and export, or add and delete by hand.
They also have a code you can put on a signup page on your site that signs players up directly at mailermailer, with automated optin. You can leave them there or take them out at will.
You can make this signup page game specific or whatever you like and target mails exactly, or target any selection and combination later.
The stats are super too, you can drill each click down to the originator.