Changing default email used for attachments?

[jonjon12]

For some reason, I can"t seem to figure out this simple thing. Whenever I send an attachment like a webpage or a photo on my Macbook Pro, the attachment is sent from an email address I do not want to use for this. How can I change the email address from which attachments are sent? (I am using Mail, not Outlook or any other client). I've tried to go into System Preferences and Preferences for Mail, and I just can"t figure out how to change this.

Thank you.