how to open a new outlook email from interface

Something like this:

a!localVariables(
  {
    a!richTextDisplayField(
      value: a!richTextIcon(
        icon: "ENVELOPE",
        size: "MEDIUM_PLUS",
        link: a!safeLink(
          uri: "mailto:xxx@gmail.com?subject=yyy",
          openLinkIn: "NEW_TAB"
        ),
        linkStyle: "STANDALONE"
      )
    )
  }
)

thank you very much, I will give it a try.

You can also use the same link in stampField(), cardLayout() based on your design preference.

Stewart Burchell How do we pass body into that dynamically like using a local variable data and how to use it such that it supports more than 2000 characters in its body.

https://www.w3docs.com/snippets/html/how-to-create-mailto-links.html

The length is limited by the operating system or the email client and cannot be adjusted from Appian.

AFAIK you cannot pass any content into the body of the email. If you want to create a fully built-out email you can do so within Appian and send directly as an email to the recipient(s). Is there a specific reason you want the email opened in your email client (which will require you to manually send) rather than having it sent automatically as described above?