If Sophos Home was installed from a different account or via an account-less dashboard, follow these steps to reinstall Sophos Home using your existing account (Premium users will  need to do this in order to keep their subscription), OR create a new account (Free users) : 

Option 1 - [Requires re-installation]

Log in to your existing account
Re-protect your computers via that dashboard. See How to reinstall Sophos Home 

Option 2- Create a new account using a different email address to keep using the current dashboard you are currently trying to access. 

1- Open your Sophos Home Dashboard from your antivirus: 

Mac: Click on the Sophos Home shield, click on … , click on Manage Devices

Windows: Click on the Sophos Home shield on your system tray, click on Dashboard

2- Once at your Sophos Home Dashboard , if you are a new user, you will be automatically prompted to Create an account, otherwise click Create Account 

3 - Follow the steps to enter an email address for the account and validate it
(see Email address confirmation for additional details) 

Note: If you do not receive the confirmation email, it was likely intercepted by a spam/junk mail filter. Check your spam/junk mail AND check your junk mail settings. You can also whitelist
no-reply@mail.home.sophos.com per your email providers' settings.

4 - Your Sophos Home Dashboard is now tied to your account, which will allow you to protect additional devices, re-install on your computer and, for Premium users, access support.

5 - To access your Sophos Home Dashboard, either use the Manage options in the antivirus, or access https://my.sophos.com and log in. 

1. Access the Sophos Home registration page
2. Enter the required details on the fields and click on Create Account.
   
3. You will receive an email confirmation email from no-reply@home-mail.sophos.com
   (see Email address confirmation for details) 
   
   Note: If you do not receive this email, it was likely intercepted by a spam/junk mail filter. Check your spam/junk mail AND check your junk mail settings. You can also whitelist
   no-reply@mail.home.sophos.com per your email providers' settings
   
   
4.  Open the Sophos Home Confirmation Email and click on Confirm Email
5. The Sign In window will open showing the Email address confirmed message
6. Enter your credentials and hit Sign In to open your Sophos Home Dashboard
7. You can now start protecting and managing your devices through your Sophos Home dashboard.
   See related information for installation steps, or visit our Getting Started Guide for additional info! 
8. 5 - To access your Sophos Home Dashboard, either use the Manage options in the antivirus, or access https://my.sophos.com to log in. 

This message indicates that the email address is already in use with a Sophos Home account.

There are 2 options to address this, follow the one that applies best to your case: 
Option 1 - [Requires re-installation] Log in to your existing account and re-protect your computers via that dashboard. See How to reinstall Sophos Home 

Option 2- Create a new account using a different email address to keep using the current dashboard you are currently trying to access. 

Please visit MFA - How to enable Multi-Factor authentication for additional security steps to help secure your Sophos Home account.