on The Book Designer:

Newsletters are widely regarded as one of the best marketing tools because your subscribers are inviting you into their inbox. While that is great, it can take time for your newsletters to convert a subscriber into a customer or client, so you will need to plan on sending out newsletters on a regular basis.
And since every newsletters you send out needs to be formatted and organized the same, it would be a really good idea to design a template for your newsletter. Not only will this save you a lot of time in the long run, you can also present a consistent message to your subscribers by setting style elements such as: