CRA indicates that eligible dividend designations can be made before the dividend payment time and by email

S. 89(14) in its entirety provides:

A corporation designates a portion of a dividend it pays at any time to be an eligible dividend by notifying in writing at that time each person or partnership to whom the dividend is paid that the portion of the dividend is an eligible dividend.

In this regard, CRA has now stated:

[T]he sending of an e-mail, with an acknowledgment of receipt, would meet the criteria 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.

Neal Armstrong. Summary of 18 December 2017 External T.I. 2017-0720731E5 F under s. 89(14).