Problems With Keychain

Running a MacPro 3,1 with OS X 10.7.3.
Using Mac default mail client.

For the past few weeks I have had an issue with the Keychain not remembering the stored passwords for my various email accounts. My email accounts will prompt me for my password, and I elect to save it to the keychain.

Sometimes this works, but lately the problem just recurs. So yesterday I purged all entries in the Keychain, and reset all my email accounts.

Then this morning I was again prompted for the password for one of the accounts, which I saved to the Keychain again.

This is annoying as I can't figure out why my Keychain is not working well.

Any ideas on how to solve this?