[mouly]

Both usages have a valid context.

In system generated messages "yours" seems more appropriate. It implies that someone else is talking to the user. If I got a message "My email was received", I would feel like talking to myself.

The UI is an extension of human brain. So labeling things with "mine" will make the UI feel natural. My contacts feels closer than your contacts.

I wrote about the same subject: http://mouly.me/2011/07/my-contacts-or-your-contacts/