1. Acknowledgement Letter: A letter sent to confirm the receipt of a payment, document, or order.
2. Confirmation Letter: A letter sent to verify, summarize, or provide the details of an agreement, meeting, or arrangement.
3. Welcome Letter: A letter sent to a new customer or member expressing greetings and appreciation for their business or association.
4. Thank-You Letter: A letter expressing gratitude for a gift, a service, or any kind of kindness or assistance.
5. Invitation Letter: A letter to formally invite someone to an event, gathering, or occasion.
6. Appreciation Letter: A letter acknowledging and expressing appreciation for outstanding contributions, efforts, or performance.
7. Congratulatory Letter: A letter sent to celebrate someone's success or achievement.
8. Apology Letter: A letter expressing regret or remorse for a mistake, inconvenience, or disappointment caused.
9. Notification Letter: A letter giving an update, a change of information, or an important announcement to the recipient.
10. Reminder Letter: A letter gently reminding a recipient about an upcoming deadline, a scheduled event, or a pending payment.
11. Follow-Up Letter: A letter sent after an initial contact, either to confirm an action or to inquire about further interest.
12. Query Letter: A letter seeking information, clarification, or additional details regarding a particular matter.
13. Order Letter: A letter made by a customer to specify and provide instructions for their desired purchases.
14. Return Letter: A letter accompanying a returned item and stating the reason for the return, usually used in e-commerce.
15. Referral Letter: A letter commending another individual or business and endorsing their service or product.
16. Cancellation Letter: A letter informing a recipient about the termination or cancellation of a previous arrangement.
17. Complaint Letter: A letter respectfully expressing dissatisfaction with a product, service, or experience.
18. Resignation Letter: A letter used to provide formal notice of an employee leaving their position.
19. Recommendation Letter: A letter offering personal or professional endorsement for an individual seeking an opportunity or recognition.
20. Love Letter: A letter written to express heartfelt emotions, thoughts, and adoration for another person.
Remember, effective routine letters should maintain a professional tone, use clear and concise language, and align with the purpose and context of the communication.