An ESP may provide tracking information showing the status of emails sent to each member of an address list.
ESPs also often provide the ability to segment an address list into interest groups or categories, allowing the user to send targeted information to people who they believe will value the correspondence.
All ESPs have the same basic features and functionality, however they vary greatly in volumes, policies, and email delivery ability, which makes the selection of an appropriate ESP critical to both the success of an email marketing campaign and the cost effectiveness of its implementation.
This is intended to result in the best possible delivery rates, with no messages blocked as spam.
According to The Spamhaus Project glossary, mass or bulk mailing is not spam if it is solicited.