Yesterday I updated to OS X 10.10.1 and now Mail is completely broken. I can't send Mail out to the SMTP server of either account. I spent a lot of time looking at this. It looks like there's a problem with the accounts. I did this with Connection Doctor open and logging the attempts to connect. An obvious problem is that when I change the information in the accounts, such as the port, and close the preferences menu, Mail asks me to save changes. I hit OK but when I try to connect again, the changes have not been saved. Adding insult to injury, Mail forgot all of my mail folders and I had to restore the Mail folder in my user->Library to a version saved by Time Machine yesterday and rebuild Mail's folders to get all of my mail back. I spent about an hour with my ISP's support when Mail did this about a month ago and the only solution was to delete my accounts, recreate them and get my Mail folders back using Time Machine. If I knew where the accounts are stored I could restore them with Time Machine and maybe this would fix this more easily than re-creating them. Is anyone else having this nightmare? Does anyone know where the accounts are stored (in some folder in my user->Library)?