MailChimp is an email marketing service provider, founded in 2001. Currently they send over 275 million emails every day. Mailchimp can be used for free with limited amount of mail and fewer features, for bigger companies they offer also paid, extended services.
Most email providers accept mail sent via Mailchimp, but in some the mail might end up direclty to the spam folder. Some services recognize these newsletters as commercial, e.g. in Gmail you can find Jolla newsletters in "Offers" inbox instead of your main inbox.
Links to subscription of Jolla newsletters are below the newsletter email. If you didn't receive the newsletter, first check your spam/offer inboxes, if it's not in those either you've probably disabled mail from Jolla in the account settings (contact Jolla care if needed).
Newsletters have several possible layouts, so they can be tuned for best viewing in desktop browsers, tablets and mobile phones. Newsletters are normally sent via email, but they can also be published in web: