It seems that some email providers deploy more than one SSL certificate per provided service (multiple servers not sharing certificates?). It would be nice to make claws-mail capable to remember upon configuration request up to a few SSL certificated per service.
This is already possible, via the hidden preference "unsafe_ssl_certs". See the manual for more info about hidden preferences: https://www.claws-mail.org/manual/claws-mail-manual.html
IMHO the proper resolution MUST include new name of the option without word "unsafe".