Email as a marketing vehicle has become increasingly valuable in today's mobile society. Its ability to increase brand awareness and loyalty with consumers is unparalleled. In fact, the Direct Marketing Association's October 2006 publication of "The Power of Direct Marketing," found that email delivers the highest ROI among marketing vehicles: $57.25 for every dollar spent on it in 2005.

What does this mean for our clients? It means that as email marketers it is our duty to make sure that our clients are utilizing it to the best of their ability.

Earlier this month I attended the ClickZ Specifics: Email Marketing conference and took away some very valuable knowledge. One thing that really stood out to me was Jeanniey Mullen's prediction that by 2009, 60 percent of emails would not be read inside the inbox. Mullen explained that the evolution of email marketing is expanding to other digital channels such as mobile devices, handhelds and RSS readers, just to name a few. Although we can't foresee exactly what the future of email looks like, we can share our existing knowledge regarding the types of channels available to clients today and the factors that differentiate them.

In today's email marketing world there are three predominant types of email messages: promotional emails, email newsletters and short message service (SMS). Although they all deliver value to the reader, each format comes with a unique purpose, set of rules and best practices.

Following are some things to consider as you try to navigate these creative waters.

Author notes: Sara Johnides is a creative specialist for Premiere Global Services. Read full bio.