http://www.emailcenteruk.com/triggered-email-marketing.php

Delivering the right email message at the right time

One of the key fundamental principles from the early days of email marketing was in delivering the message at the right time.

This is still true today but the theory is less about what time or day of the week to launch a newsletter but when is the optimum time in the customer lifecycle for each individual to receive a message.

Typical examples of this are:

• Reminders to renew a subscription 30 days before expiry
• Emailing an incentive to make a further purchase to those that have gone 6 months since their last purchase
• Alert a user who has left items in their shopping cart for 24 hours but has not completed the purchase
  http://www.emailcenteruk.com/triggered-email-marketing.php