Can't completely remove old email addresses
I purchased my MacBook Pro from a friend recently. I removed her email accounts from the mac mail, but it still insists on trying to send all of my emails from one of her accounts. I am able to manually change it when I am composing a message, but have almost forgotten on several occasions, which just would not be ok! I have gone into preferences to try and tell it which email address to send new messages from, but in the drop down it only gives me the option of one of hers or "send from selected mailbox" - my email address is not an option as the default, and it still tries to send from hers when I have "selected mailbox" chosen.
I am on a 2011 MacBook Pro running Yosemite 10.10.3
Any ideas?