This is one of the current hang-ups that delayed the mandatory compliance date of the regulations. While I too believe it could be made a contractual issue, others did not necessarily agree and want to ensure taht adequate consumer protections are built in.
The current regulations, which are optional at this point, say that you have to use a non-proprietary e-mail notification system. That is, you can't just notify them with a message when they log into Internet banking.
If you get return e-mail, you'd need to use an alternate address. Likely this means you'll have to snail mail them, possibly inserting a copy of the statement to promote timely delivery. Remember those cost savings you were going to see with e-delivery, it just left.
So the bottom line to your question is, there isn't a solid answer or enough folks doing this to to be considered a best practice. And whatever you do may have to be changed when the regulations do get finalized. So whatever you do, make it flexible.
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Andy Zavoina
Opinions stated are not necessarily that of my employer.