E-Mails as Debt Collection Letters

There's an interesting collection comapany based in San Francisco called True Accord which only sends collection letters via e-mail.

Does anyone have experience with respect to our e-mails are considered as initial and ongoing written communication from a debt collector under the FDCPA and state laws?  Are they legally valid without proof of delivery?

I've never seen a collector do this before.  They never execute traditional written correspondence.  All collection attempts made via e-mail.