We're so happy to welcome you to the family! A "thank you for joining" membership letter should include a personalized greeting to the new member.Use the member's first name in your salutation. I wanted to share an open letter to my future daughter in law. Here are 10 things your welcome letter or email to new members must include plus a template that can be customized for your organization. Letter to my new daughter in law. Discover Pinterest's best ideas and inspiration for Letter to my new daughter in law. 1. Enter the date at the top of the letter. If you are coming on the program for the first time, congratulations and welcome! New member welcome letters are the perfect way to introduce your organization, reiterate its values and mission, drum up excitement, and express your gratitude.