In Secura Insurance Co. v. Illinois Farmers Insurance Co., 232 Ill. 2d 209, 902 N.E.2d 662, 327 Ill. Dec. 541 (2009), the plaintiffs' notice of appeal was filed by mail and received by the circuit court four days after the 30-day filing period had ended. Secura at 6. The plaintiff did not, however, include a certificate of service or affidavit indicating the date of filing with the circuit court clerk. Secura, at 1. In response to defendant's motion to dismiss the appeal for lack of jurisdiction, the appellate court allowed the plaintiff to supplement the record with a letter to the circuit court which was dated on the final day of the 30-day filing period and then denied the defendant's motion, ruling that the court was not deprived of jurisdiction because the failure to comply with the rules was harmless error and there was no showing of prejudice to the defendant. Secura, at 6. The supreme court reversed and held that the defendant's mailing, which did not include a certificate or affidavit of mailing, failed to fulfill the requirements of proof pursuant Rule 12(b)(3). The court noted that a party must file a proper proof of mailing as required by Rule 12(b)(3) in order to take advantage of Rule 373 because without such proof of mailing "there is nothing in the record to establish the date the document was timely mailed to confer jurisdiction on the appellate court." Secura at 10. The court found that the cover letter to the circuit court submitted by the defendant did not provide proof of mailing such that it was competent evidence under Rule 12(b)(3) because the letter did not "contain an affidavit or a certificate and nothing was certified or sworn to." Secura at 11. The court further found that the "Notice of Filing" was not sufficient proof because the certificate of service attached to it indicated only that the notice of filing was mailed to the plaintiff's attorneys on the date the notice of appeal was due and there was "nothing in the certification or in the body of the notice of filing that attested to the mailing of the notice of appeal to the clerk" on a timely date. Secura at 11. In distinguishing the cases upon which the appellate court relied, the court noted that the issue in the case before it was not "merely about a slight defect in the form of the notice" and that the case did not concern a certificate or affidavit that was submitted but that had a typographical error, misspelling, or other inadvertent mistake. Secura at 12. Rather, the case concerned the defendant's "failure to prove by certificate or affidavit that it complied with the jurisdictional 30-day notice requirement in Rule 303." Secura at 12. Finally, the court stated that harmless error was not applicable to the case because the appellate court did "not have the authority to excuse the filing requirements of the supreme court rules governing appeals." Secura at 13.