Windows guides
How to Add a Non-Microsoft Email Account to the Windows 8 Mail App (Historical)
Historical Windows 8 Mail app guide to adding another provider account through Settings > Accounts > Add an account.
THE JOURNAL
mail app
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Troubleshooting
Unable to Sync Outlook.com in the Windows 8 Mail App — Historical Workaround
Historical Windows 8 Mail-app troubleshooting for Outlook.com account synchronization, with current status of the retired Mail app and service changes.
Windows guides
How to Add an Email Signature in the Windows 8 Mail App — Historical Guide
Historical Windows 8 guide to adding an email signature in the original Mail app using the Settings charm and account options.