After sending an email from UpMail, you'll have the capability to view the email as a webpage or generating a link/URL.
All sent emails are accessible in the Emails section which can be accessed from the top menu. Click on the specific email you would like to view as a webpage.
Select the 'View' option.
The email will open as a webpage and you can copy and paste the URL from here. Alternatively, you can select 'Copy' from the previous window.