When you upgrade OS X, the accounts you have configured in the Internet Accounts system preferences should migrate and be just as usable as they were before upgrading. However, there may be times when calendars won’t load, e-mail messages may be missing, or you otherwise cannot access your accounts. While specific problems can be individually investigated, if they are nondescript and affect multiple accounts, you can try re-migrating your user account from a backup. Continue reading ⇒