I didn't find it in Reg E but if you look at Fed's circular letter 533-01 5-7-01, under "Providing Timely Disclosures" it states "Disclosures delivered electronically must comply with existing timing requirements under EFTA & Reg E. See, for example 205.7(a), 205.8(a)(1), and 205.9(b).
205.9(b) deals with periodic stmts.
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Opinions are my own and not of my employer.