PostOffice is an excelent massmailer,
Auto add new emailaddreses,
Auto remove emailaddresses,
Auto delete bounced emailaddresses,
Auto check for new messages,
Handle mutiple mailinglists,
Auto replay when Subscribe,
Auto replay when Unsubscribe,
Send Plain or Html messages,
Send Attachement,
Excluded list,
Import mailinglists,
Auto check for dublicates,
Auto notify when new version is avalible,
Auto add Un/Subscribe info in email