According to marketer Dan Kennedy, what others say about you is about one thousand times more believable than what you say about yourself. I have found this to be true, especially on the internet where people may live halfway around the world from you.
Whenever someone emails you with a compliment about what you are doing in your business, ask them right away if you can use what they said as a testimonial. Most people are happy to let you use their comment, along with their name, city, and website. You can include one or two of these in your emails to let the rest of your list know how others feel about you and what you are doing.
I keep a file with testimonials so that I can use them in emails and on my sales letters. The very best testimonials are based on the results somene achieved with you, rather than those that just say how wonderful you are. You decide which ones to use to let others get to know you better.