There is no single simple answer to this.
For a start you have to realize that emails have no concept of 'pages'... they are just continuous streams of content, so it's unlikely you can replicate your '4 page newsletter' in an email. The best you can do is approximate it, but it's going to get really confusing if you have articles that cross the spread or are continued on separate pages.
Second to that, 'styled' (i.e. non-plain text) emails use HTML for formatting, so you need to convert your Pages document to HTML. There's no one-click option for this. The best you're likely to get is by copying all the content from Pages and pasting it into a new email message (plus some clean-up). Have you tried that? how did it work out?
The advantage of this approach is that non-visual mail clients will still see a text-only version of the email.
The other option is to 'print' each page as a separate image (e.g. JPEG) and insert the 4 JPEG images in the email message. This will guarantee your formatting/layout, even if it's a little tricky for users to navigate... and non-graphical browsers won't see any content.
At the end of the day, you're still at the mercy of the recipient's mail client, each of which may have different options for viewing rich content.
So even today, bridging the physical (printed/hard copy) and digital/email worlds is still a bit of a black art.