[Refactor] Mailing / Suspend System

[AGuyNamedJens]

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💡 Description

The complete Refactor of the Mailing System will fix several issues, as well as the addition of COMPLETE Mail customization

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Progress:

• Create new Services related to emails
• Create templates using {variable}'s
• Create tooltip option in Settings
• Implement all email methods
• Implement customization fields
• Fix "Server name missing in notifications" [Bug]: Server name missing in notifications #833
• Implement "Remove Salutation and Closing from email notification" using Customization options Remove Salutation and Closing from email notification #387
• Implement "Notify the user 3 days before servers are suspended" Notify the user 3 days before servers are suspended #255
• Implement "Send notification when servers were unsuspended" Send notification when servers were unsuspended #248
• Fix "Don't send notifications to suspended users" [Feature] Don't send notifications to suspended users #918
• Implement "Better Server Suspension" [Feature] Better Server Suspension #978

Other Notes:

After the following has been done, the following should be done:

• Redo suspension system

• Suspension and Unsuspension fully automated
• Warn when server about to be suspended (1M, 1W, 1D, 1H before (only once unless renewed)
• Warn at 100%/66%/33%/0%(unrecoverable) about deletion (only once unless renewed)
• Adjustable deletion time after suspension
• Additionally:
• Update all affected servers when product configuration changed
• Email affected users with product with (newly made) template telling them the new specification change

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🛠️ Type of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (a fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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🖼️ Screenshots (if applicable)

Soon.