• 5 The defendant is not entitled to have the judgment vacated on the strength of his having moved or on the basis of the mere fact that the registered letter containing the summons was returned unopened. As pointed out in Duke v. Paul (1974), 20 Ill. App.3d 500, the defendant's contention that he did not receive the copy of the summons by registered mail does not automatically open the judgment. As the court said in Duke:

I am left with doubt as to what any competent and diligent attorney could or should have additionally done to locate Dyer. There is no question in this record that Dyer left Wyoming, left his sister without notice or later contact and disappeared from his last known address which was his sister's address at the trailer court. Due diligence in this case would conform to the standard of effort approved in Sommers v. Gaston, 295 A.2d 578 (Del.Super. 1972) where plaintiff checked all available sources but with no success. See also Duke v. Paul, 20 Ill. App.3d 500, 314 N.E.2d 517 (1974) and Pelay v. Ploog, 281 Or. 59, 573 P.2d 1229, 1231 n. 2 (1978). I am also left with the question about waiver at some point in the technical aspects of service of process by entry of appearance and pretrial pleading activities as a participant in the litigation.

We do not believe this constitutes the type of information upon which one may leap to the conclusion that defendant is a nonresident of Illinois. • 6 The facts of the present case stand in sharp contrast to those in Duke v. Paul (1974), 20 Ill. App.3d 500, 314 N.E.2d 517, where plaintiff's attorney submitted an affidavit of defendant's nonresidency based on information and belief after he had made personal inquiries and was told that defendant had moved from the State. Here, the sheriff's returns relied on by plaintiff never suggested that defendant was not a resident of this State during the times in question.