Is it a good idea to list your board members on the letterhead in your direct mail?
Short answer: Probably not.
There's a useful look at this often-asked question at Bloomerang: Should Nonprofits List Board Members In Their Letterhead?
The reason not to do it is this:
... it takes away from one of the most foundational elements of good donor communications: making your letters and emails all about the donors.
When you list your board, you are nodding, however slightly, at their heroism. Just a little jarring note in your otherwise beautiful symphony of donor love that I know your fundraising is.
It might be a good idea to include a board list in a couple of situations: If you are in a very small and/or tight-knit community, the kind where everyone knows everyone else. Meaning virtually every name on your board will be known by virtually every donor you're talking to. In that case, the board list might be a useful form of "social proof." It might have a similar impact with subsets of your donors, like major donors. Will virtually every donor know virtually every board member?
Some organizations have one or a few "famous" board members they want to tout. I'm not sure printing a list of 20 people in hopes that the famous ones will be noticed is that effective. Instead, you could have your celebrity board member sign the letter. Or a lift letter.
Whatever you do, don't fall into the trap of using your fundraising to recognize or reward board members for their service. There are other ways to do that that will not decrease your fundraising revenue!