1 answer
Under the email administration section in setup there is a setting called "Organization-wide Addresses".
You can add the secondary address here and choose which profiles can use it.
Once the email address is verified (you need access to the inbox) it will become available for selection when you send an email.
A "From Address" option will appear at the top of the salesforce email editors for all users that the address has been enabled for on their profile.
