Since the user has known they are Moving their Main E-mail account away from on e-mail provider to another E-mail Provider and has known there has been a 3 Moth Grace Period before the Old Account will be closed.
Is there any specific reason that during that 3 Month Grace Period they have not Notified ALL the Important Entities in advance of this pending Change in e-mail address ?
Usually and like when I have physically move from House to House, I have contact ALL the Important Entities in Advance of the change of Address.
This same principle would apply to changing e-mail addresses
As for E-mail rules and as perviously mentioned, the rules will, at some time, become obsolete once the Old e-mail Account is Closed