Define a stub of the MailSpoolMailSystem class
Place module into 'mail' package
Define activation and deactivation functions
Add install file with necessary hooks
Define mail_spool_is_active() and use in other funcs
Define mail_spool_discover_mail_system()
Define mail_spool_send_mail()
Implement hook_schema()
Define constants with spooled message statuses
Store spooled messages to DB when they are sent
Create a separate inc-file with message crud operations
Define a function to load next spooled message
Define function to change a message status
Do not display message to user when spooled message has errors
Implement hook_cron() and send spooled messages
Delete another module variable on uninstall
Implement hook_requirements()
Define a function to count spooled messages
Change default severity for spooling status report
Add 'value' key to requirements info