You can set / edit your communications email addresses in the Company details:
In the Web Portal go to: Admin > Company Details.
There will be three different email address that you will need to complete.
Email From: This is the email address that will appear in a client's received email as the address that the email's been sent from.
Reply To: This is the email address that a direct email reply from a customer will be sent to.
Company Email Address: This is the email address that appears on invoices, quotes, and other PDF communications that are viewable by your clients.
After you've edited the company email addresses to your preference, select Save.