Mailster offers by default two delivery methods:
Additionally you can add more methods with plugins.
This is the default method and is not recommended for bulk mailing in general. Often providers limit the amount of mails which can be sent with this method to prevent spammers. Talk to your host about the limits and if you are allowed to send bulk mails. Problems?
This is the method you should use if you have many subscribers. Contact your host for the credentials. SMTP requires certain ports to be open. Problems?