I can not open Mail (version 4.2) after my upgrade (10.6.8)

The Mail version you want is 4.6 (1085). Your update to 10.6.8 should have been followed by a Combo update and a software update to pick up the security additions.

Mac OS X 10.6.8 Update Combo v1.1

I don't understand why not. Mail 4.6 is a natural part of the Combo update. I am linking you here >>> to another series of posts dealing with the same subject. The only thing different to what I advised you is to repair permissions. That may be subjective as there are two distinct viewpoints. If you dig around for a while in 'More like this' (to the right of these posts) you may find something more.

Please help - I installed automatic...: Apple Support Communities

I shall be away now for the next ten hours.

By then I hope you'll be sorted. 🙂

Mac OS X v10.6: Mail.app won’t open, or "You can't use this version of Mail…" alert after installing Security Update 2012-004:

http://support.apple.com/kb/TS4424?viewlocale=en_US&locale=en_US

Fellow user Grant Bennet-Alder offers this solution:

Some users have reported this problem if the Mail Application has been moved out of the top-level /Applications folder, or duplicated in another location.

When the Security Update is done, the old version of Mail is disabled.

The solution has been to:

1) make certain Mail is in the /Applications folder

2) There is no other copy anywhere else.

3) Once steps 1 and 2 have been done, Manually download and re-apply the Security Update (2012-004) by hand.

Security Update 2012-004 (Snow Leopard)

If the Mail.app has been LOST, it can be re-installed by applying the 10.6.8 version 1.1 combo update. But this update is quite large and it is usually not necessary:

Mac OS X 10.6.8 Update Combo v1.1

Glad to see it's sorted. 😀