Hi Wzzz,
I'm been having the same issues as Patriciados and have followed your advice, which has worked sort of. Here's my situation; if you could shed some light on how I can resolve This mail issue, I would be so grateful.
Ran the security update but had Mail on my desktop, not in Applications folder so it did not update. Put it back into Applications folder, tried to run the update again (from the downloadable file on support) and it still didn't work; new mail did download but when I clicked on it to launch, it just wouldn't open. So, I went back in to Time Machine and restored a version of Mail from a few days ago, replaced the "new" mail with the "old" mail in applications and ran the update again. This time it did appear to work! But, there is a new issue that has arisen.
When I launch mail from the applications folder, the icon goes down into my dock and shows that I have messages waiting. However, it will not launch "open" so that I can view and respond to messages. The navigation bar at the top changes to the mail navigation bar but the window won't open. I clicked on Window-Message View and this successfully opened the mail however, some messages would not open and others would not show any content. Since closing it down, I cannot even open the window using the Window-Message View as I did before, mail will not "quit" and the icon remains in my dock showing that new messages are waiting.
Should I go through the whole process again, restoring an older version, replacing new with old, doing the update and hope for the best? I am missing something?
Thanks so much.