Deleted Mail Keeps Re-Appearing with BT Yahoo Mail IMAP

I have addressed this issue to the BT Community, but no suggestion has helped.

Until recently I had no problems with using my BT Yahoo Mail IMAP Account on my iPad/iPhone and iMac. Now all of a sudden when I delete emails on the iMac they often come back into my Inbox. Having read a few suggestions on the web I changed my Preferences on the Mail>Preferences>BT Internet IMAP>Maibox Behaviours for Trash from On My Mac Trash to None, but there are still instances of deleted emails bouncing back to my Inbox. Another suggestion was to change the Server Settings to a Yahoo based setting or even an Apple based setting. I am loathe to do this as all seems well on the iPhone and iPad and these are the settings I have used for many years without a problem. I was advised on the BT Community site that changing to Apple setting would not work and changing to Yahoo settings would be a temporary fix at best. I am also experiencing an occasional issue whereby all my folders disappear. I remedy this by by disabling and re-enabling the "Enable This Account" setting under Preferences>Account Information.

Webmail is working fine, the issue is the iMac alone and this is my main method of email work. I know I can go onto BT webmail and delete the emails from there, but I have been able to deleted via my Apple Mail client for at least 3 years with no problem.

Another older suggestion is that I opt for mail to deleted from the server immediately, but that setting no longer seems to exist on my High Sierra.

Any suggestions very welcome.