It's strongly advised to create a good all purpose business letter for routine correspondence. Writing original letters for each case isn't cost effective, and wastes a lot of time.
You can use standard paragraphs for your business, addressing routine issues. This is easy to do on macros, and can also be used as quality control to ensure all correspondence is consistent.
You should leave space for additional materials which are non routine, but remember to check the additional materials for content before issue.
The example below is a standardized letter from a white goods supplier to a customer regarding warranty and a potentially dangerous product safety issue.
Warranty claim and safety issues regarding your appliance.
I refer to your letter / email of (date) concerning your Samsong XII toaster oven.
The warranty for these products is 12 months from date of purchase. This warranty was activated on (date) and is therefore outside the 12 month time frame. We are happy to arrange for servicing of your appliance, but standard service fees will apply.
We note with concern your information regarding the safety of this appliance, and we appreciate your bringing this matter to our attention.
It is suggested that you return the appliance to our local outlet in your area for examination. (Please bring a copy of this letter to the local store for reference.)
Our policy regarding unsafe appliances is that you may request either a full refund, or exchange, if the appliance is proven to be defective.
(Non standard paragraph)
Notwithstanding the warranty issues and time frames described above, if the appliance is found to be faulty as a result of any defects at the time of purchase, we will repair or replace the toaster oven at no cost to you.