How to update the contact email address for your Clientnet / Messagelabs user
Once logged in, you can click on the profile icon at the top right of the page to access your user account information. The address can be changed on that page.
If your user is a portal user(linked to a Broadcom/Symantec account), then the email address will not be able to be edited unless you click the button to "Disassociate Login" first:
After your Broadcom/Symantec account is disconnected, you can update the email address and then associate your Broadcom/Symantec account again.