Acquire new readers through word of mouth or e-mail referrals. Don't buy e-mail lists. Let your current readers know that it is o.k. to forward your e-mail news to their friends and business acquaintances. Welcome new readers as they join. If you can, and it is feasible, let current members of your e-mail community know the names of recent subscribers.
Human beings are, as a whole, optimists.
If someone wishes to be removed from your e-mail community building efforts abide by their wishes and let them know you have removed them. And do it right away. They can always rejoin later as many will do. Don't abuse the power of e-mail once you have created a successful email franchise. It is a very fragile thing.