If you have questions about using mojoPortal, you can post them here.
You may want to first review our site administration documentation to see if your question is answered there.
Can I make the field email adress optional while commenting at blog module? I don't want to make people tell me their email addresses if they don't want to.
Users who have signed in to your site will not need to enter an email, but it sounds like you do not want that. You can also use Facebook comments or Disqus or IntenseDebate, instead of the mojoPortal comments system. Each has its own pros and cons. IntenseDebate does not require users to enter anything other then a name, so might suit you. I've not tried Disqus.
Hope this helps