But are you talking about an E-mail LIST you made and placed on your site or what
If you have that you get one newsletter you can send out a week or such if you have the free version if you have the upgraded version probably can do more.
As I don't use this service use something can control more for this kind of stuff
You just got to watch what you are putting in your newsletter you send out when people join your mailing list.
Only put in it what you want. I find it stupid to subscribe and unsubscribe
My experience is that how a message looks when created and previewed is not necessarily how it is rendered by the recipients email reader.
The most reliable test is to use several email accounts which use different software so that you can be sure that people are getting a consistent view.