I upgraded without a problem. Now all my accounts have a triangle and ! warning. I cannot send or receive email. I am on Sierra with Mail 10.0. If I quit SpamSieve, it remains frozen.
I’ve not received any other reports of this happening. Please explain more specifically what you mean by “lock” and “frozen.” Are you able to access the menus in Mail? Have you tried restarting your Mac?
Also, please see this page about hangs.