Generally, you want its autolock time to be longer than the email checkin time. In the settings dialog, check the autolock settings for the keychain if it's set to lock after, say, 5 minutes, and Outlook checks for incoming messages every 10 minutes, the keychain will lock between each check. With the login keychain still selected, choose Edit menu > Change Settings for Keychain 'login'.If it finds (& repairs) any problems, check to see if that's solved the problem. Open Keychain First Aid (under the Keychain Access menu), enter the user's account password, select Repair, and click Start.Select the 'login' keychain in the sidebar, then run some checks: If the keychain list isn't shown in the sidebar, choose View menu > Show Keychains.

Run the Keychain Access utility (from the user's account). There may be something off in the way the user's password is being stored in their keychain.