Open your email anytime and it is sure to have a message or two that you simply do not find useful. All too often though, there are companies sending messages that make you ask, "did I ask to be spammed?" I like to have updates from the brands I use, it is helpful, helps me remember what is going on, and hopefully provides monetary benefits to being one of the customers who is on the list.
Take a look at the messages you are sending your customers. Ask yourself honestly, does the content represent a significant value to them, or to you? Most of the time we will find that the message is more about us than the customer. This will often result in the customer feeling we are just providing spam.
You may not see that perception from the number of lost fans or customers leaving your mailing list. Many will just ignore, delete without reading, or hit the "mark as spam" button on their email program. So it is always important to remember who keeps you in business and put yourself in their shoes. Your brand reputation depends on it.