Inspiration

Sign-up flows
Getting an opt-in
Re-opt-in after rejection
Collecting user data (post signup)
Collecting email addresses
Discount reminder (post signup)

Transactional flows
Order confirmation
Order tracking
Collecting user data (post order)
Double opt-in (post order)

Retention & revenue flows
Repurchase discount
Conditional retention messages
Cross-selling
Up-selling
Loyalty program
Order reminder
VIP customers
Brand/product introduction