I made a few changes to my imap server (dovecot) and now kmail is
mis-behaving.

It won't believe me that I'm OK about the certificate I generated.

On every start-up of kmail

The server certificate failed the authenticity test (hostname ...)
(I choose continue)

Would you like to accept this certificate forever without being
prompted?
(I choose forever)

it doesn't believe me.

Where should I look to fix?