Apart from what is said above, which is all valid:
One thing that matters is the email server software you are using on your web server.
Exim or Qmail (Fully Patched) should be fine.
I wouldn't suggest sending out from any server unless it was your own dedicated server and make sure that you have all the DNS SPF records in place.
Setting Up SPF DNS Records
Apart from this, i don't think there is going to be much difference between using a big email provider and one on your own domain for a small amount of emails being sent.
If you are sending thousands you will definitely need a dedicated server.
I use aweber for ease of use at the moment.
Also, if you put a disclaimer at the bottom of your email most people will not read any further - you can hide your opt-out underneath this.