[NAME, COMPANY AND ADDRESS, ex.
John Smith
XYZ Inc.
1234 First Street
Suite 567
Anycity, Anystate  85245] 

Dear [NAME, ex. John Smith],

It has been a pleasure to serve you in the past, and we look forward to doing business with you in the future. 

I am writing you regarding a change in our policy.  [MENTION RATIONAL BEHIND CHANGE AND HOW IT MAY, IF AT ALL, BENEFIT CUSTOMER, ex. To continue to offer you reasonable and competitive prices, we have amended our terms of sale to stipulate that we are not responsible for goods damaged while in shipment.  Fortunately, this will enable you to select any freight company who will best serve your interests.]

Indeed, we will continue to serve you to the best of our abilities.  Please call me at XXX-XXXX if I may be of any service to you. 

Sincerely,

[YOUR NAME, ex. Jill Jones]