general

• http://write.flossmanuals.net/thunderbird/about-thunderbird/
• https://support.mozilla.org/en-US/products/thunderbird
• folders and filters
• customize, controls, etc
• window layout

specific

• nostalgy, mail summaries, layout, date format, etc
• enigmail, external editor, etc

test/cycle

• ColumnsWizard
• Thunderbird Conversations
• One-by-One Forward