In this post, Loren McDonald makes the point that even though transactional messages are a golden opportunity to engage with customers (to introduce or extend the email relationship with customers or subscribers, to anticipate and answer questions or to cross-sell or up-sell products or services), many marketers don't take advantage of this easy and obvious benefit.

He offers some best practices for your transactional emails:

1. Move responsibility for transactional emails into the marketing department.
2. Set up your transactional message stream on a separate IP address.
3. Redesign the inbox presence.
4. Position the transactional message content front and center in the message body. Use HTML design elements to create an attractive and organized message.
5. Add personality that supports your brand or company image, expresses your thanks for that they're customers and invites them to engage further.
6. Use the transactional message to initiate or expand the customer relationship.

Read more here.