Thanks, I have reinstalled the OS in Recovery to see if that did anything. Still missing the emails.
I can't see how to restore Mail from my Time Machine backups.
In recovery mode I can choose to restore from Time Machine, but the last Full backup was June 2020, when I did the first backup. If I enter Time Machine from my desktop I can go back a few days before the issue with Mail but I can't open the Mail application, I get the message 'You can’t open the application “Mail” because it is in a Time Machine backup.' I not sure what I'm trying to restore, as my mail is in iCloud and the missing emails are also missing if I log into Mail at iCloud.com .
Sorry if I'm being stupid, but I don't really want to restore everything on my iMac if I don't have to. I'm sure this is ultimately an iCloud issue given the discrepancies between Mail on my iMac and on my iPhone.
Any other ideas? Can I uninstall then reinstall Mail? I've tried rebuilding my inbox. I only use one email address and that is enabled iCloud IMAP and is showing status as online.
In any case, why would any of my mail settings have changed without my knowledge?
Looking forward to hearing from you.
Kind regards