Click Personal > Profile.
Click Edit at the top-right of the page.
In the "Contact Email" field, enter the email address you would like to email patients from.
Click Save Profile.
This will change the email address used to email patients for your currently selected practice group without affecting your Halaxy profile in any other way.
Note that your contact email address applies only to the currently selected practice group. You can set a different email address for your other practice groups by selecting a different practice group in the top-right and going through this process again.
For more information on how to customise your contact email address, please see Email Sender Preferences.