(a)In general. Except for correspondence submitted via the U.S. Patent and Trademark Office (USPTO) patent electronic filing system in accordance with § 1.6(a)(4) , all correspondence intended for the USPTO must be addressed to either "Director of the United States Patent and Trademark Office, P.O. Box 1450, Alexandria, Virginia 22313-1450" or to specific areas within the Office as provided in this section. When appropriate, correspondence should also be marked for the attention of a particular office