Okla. Stat. tit. 12, § 12-1755: Service of affidavit and order upon defendant

Unless service by the sheriff or other authorized person is

requested by the plaintiff, the defendant shall be served by mail.

The clerk shall enclose a copy of the affidavit and the order in an

envelope addressed to the defendant at the address stated in said

affidavit, prepay the postage, and mail said envelope to said

defendant by certified mail and request a return receipt from

addressee only. The clerk shall attach to the original affidavit

the receipt for the certified letter and the return card thereon or

other evidence of service of said affidavit and order. If the

envelope is returned undelivered and sufficient time remains for

making service, the clerk shall deliver a copy of the affidavit and

order to the sheriff who shall serve the defendant in the time set

in Section 1756 of this title, or at the election of the plaintiff

service shall be governed by the provisions of subsection C of

Section 2004 of this title.