Imprisoned when their father died, David and Steven Jacob relied on the mailbox rule and a “belated proof of service” to save their appeal in a will contest from being tossed as tardy by the Illinois Appellate Court.They mailed the notice of appeal from prison, but there was no postmark on the envelope, and the clerk’s office file stamped it as having been received 41 days after a final judgment dismissed their complaint against their sister.The notice of appeal was accompanied by a combined notice of filing and proof of …