Can PS be used in an official letter?

Yes, "PS" (postscript) can be used in an official letter, but it should be done sparingly. It is typically used to add an afterthought or additional information that wasn't included in the main body of the letter. However, for formal correspondence, it's often better to incorporate all relevant information within the main text to maintain professionalism. If used, ensure that it aligns with the tone and purpose of the letter.