I can't say this strongly enough: DO NOT UPGRADE to IOS 26 without reading the hundreds of reports claiming that long deleted Mail messages and Message messages are completely restored along with the new OS.
Either you delete them all one by one again, or reset the phone. READ. Where they been kept?
Apple Confirms iPhone Decision—You Must Upgrade iOS 18 To iOS 26.2 Now
Apple issues an upgrade now warning to millions of iPhone users. iOS 18.7.3 is not available.
