18 December 2017 External T.I. 2017-0720731E5 F - Eligible dividend designation -- summary under Subsection 89(14)

CRA stated:

[T]he sending of an e-mail, with an acknowledgment of receipt, would meet the conditions for the designation of a dividend as an eligible dividend pursuant to subsection 89(14).

As to when the written notice must be sent and dated, the CRA accepts that notification in writing should be given to shareholders between the time the dividend is declared and the date the dividend is paid.