The problem the power solves. Section 2503(b) excludes a limited amount of gifts to each recipient each year from taxable gifts, but the exclusion does not reach a gift of a future interest. Treasury Regulation 25.2503-3(a) says no part of the value of such a gift may be excluded, and defines a future interest to include "reversions, remainders, and other interests or estates, whether vested or contingent, and whether or not supported by a particular interest or estate, which are limited to commence in use, possession, or enjoyment at some future date or time." A contribution to a trust that will pay the beneficiary years from now fits that description exactly.
Paragraph (b) of the same regulation supplies the test the power is drafted to satisfy: "an unrestricted right to the immediate use, possession, or enjoyment of property or the income from property ... is a present interest in property. An exclusion is allowable with respect to a gift of such an interest (but not in excess of the value of the interest)." The regulation's own examples make the point unforgiving. In Example (1), income the trustee may withhold at its discretion is not a present interest and no exclusion is allowed at all. Example (2) is the life-insurance case specifically: policies transferred to a trust whose income will not begin until the grantor's death are a gift of a future interest.
What the power looks like in the instrument. Each time the grantor contributes, each beneficiary named as a holder of the withdrawal right may take a stated share, usually in cash, for a defined window that is often 30 days. The right must be genuine. A right that the trustee can defeat, or that the beneficiary has no practical way of exercising, is not an "unrestricted right to the immediate use" of anything.
Why the letter exists, given that no rule requires one. Neither section 2503(b) nor Treasury Regulation 25.2503-3 mentions a notice, a letter or a delivery requirement. The practice grew up around the regulation's own language: a right the holder does not know about, and cannot exercise before it expires, is difficult to describe as unrestricted or immediate. So the standard is a dated written notice to each holder at each contribution, kept with the trust records, stating the amount, the deadline and how to make the demand. For a minor, the notice goes to the parent or guardian who would act on the child's behalf.
The lapse, which is where the mechanism bites back. When the window closes unexercised, the beneficiary has allowed a power of appointment to lapse. Section 2514(e) provides that a lapse "shall be considered a release of such power," but only to the extent the property that could have been appointed exceeds the greater of $5,000 or 5 percent of the assets out of which the lapsed power could have been satisfied. Section 2041(b)(2) says the same thing on the estate tax side. Both figures are fixed in the statute and are not adjusted for inflation, which is why the shorthand "five-and-five" has outlived several decades of price changes.
A release above that threshold has two consequences for the beneficiary, not the grantor. The released amount is treated as a transfer by the beneficiary to whoever else benefits from the trust, and because that transfer is usually a future interest to the other beneficiaries, it does not qualify for the beneficiary's own annual exclusion. And the beneficiary may end up with a slice of the trust in their own gross estate under section 2041. The standard drafting answer is a hanging power: the withdrawal right lapses each year only up to the five-and-five amount, and the unlapsed excess carries forward, hanging over the trust until later years absorb it.
Two further points. The five percent prong is measured against the assets from which the withdrawal could actually have been satisfied, so in a trust whose only asset is a life insurance policy with modest cash value that prong can be very small, leaving $5,000 as the operative figure. And a separate route exists for gifts to a minor: section 2503(c), with its own regulation at 25.2503-4, treats a gift to a trust for a person under 21 as a present interest on different conditions entirely, including that the property pass to the beneficiary at 21. It is an alternative to a Crummey power, not a companion to it.