45 CFR §2105.25

1. (a)Except as outlined in § 2105.27, an Agency must promptly notify a submitter in writing when it receives a FOIA request if:
   1. (1)The requested information has been designated by the submitter as confidential information under § 2105.24(a); or
   2. (2)The requested information has not been designated as confidential information by the submitter under § 2105.24(a), but the Agency identifies it as possibly confidential information.
2. (b)If a voluminous number of submitters are involved, the Agency may publish a notice in a manner reasonably calculated to reach the attention of the submitters (for example, in newspapers or newsletters, the Agency's website, or the Federal Register) instead of providing a written notice to each submitter.