The standard plan comes with as many POP3 accounts as you want.
It comes with 1 mailing list, they are the kind where you get an e-mail address for the list, and you send e-mails by e-mailing the address.
For example, e-mailing
mylist@mydomain.com , it would send out the e-mail to everyone on your list.
Extra e-mail lists are available for $2.50 per list per month.
However, if you like, you could setup a mailing list program with a script on your webpage, and there would be no limit to how many you created.
It would be the kind of mailing list where you would send out the e-mails through a form in your webbrowser.
I hope this answers your questions.