Probably stating the obvious, but:- - will your email newsletter include details of how to unsubscribe? - will the unsubscribe system actually work if the recipient doesn't know their username or password (ie. they can just say "don't send any more to this email address")? - will the email be sent out BCC, so that subscribers don't see other subscribers' emails?
I've subscribed to a few mailing lists which have hit these problems. Manually-run lists are mostly OK, but automated ones can be a pain if they're not set up right. A particularly bad example was the Archers Addicts group which my wife subscribed to (on my email address) and then wanted off when she got her own email address. She couldn't remember her login details, there was literally no way to unsubscribe under the automated system if you didn't know your login, and the admins weren't interested in helping. I had to threaten them with a formal complaint to their ISP under anti-spamming rules before they took any notice. :-(