Best Email and or Blog Campaign

I am building a SquareSpace site for my fashion footwear consulting and sourcing company. I am interested in any campaign software where the newsletter can also appear as a  blog post, as circled in red "The Capsule" per page design attached . I would like a pop up window to collect addresses that would integrate with a newsletter app such as SqSpace Email, MailChimp or FloDesk, where the content is created and then emailed to subscribers. Can the newsletter content simultaneously update as a blog post? What is the best way to set this up? I would like the content on my blog posts to be equivalent to what's in the newsletter.